When Apple launched the iPhone App Store in 2008, few people recognized how revolutionary it was. Four years later, everyone can see that the App Store has uprooted the software industry, creating an app craze that has spread far beyond smartphones.

Now, the app-store model is taking over desktop PCs. Apple launched its Mac App Store in January 2011, and has already seen more than 100 million downloads in that marketplace. With the debut of Windows 8 later this year, Microsoft will launch the Windows Store, the company's first centralized location for desktop and tablet apps.

To find out how app stores are changing desktop software, PCWorld spoke to software makers and research analytics firms. Not surprisingly, many developers are enthusiastic about the easy distribution and streamlined billing that app stores provide, yet these stores also introduce challenges--some that are unique to desktops, and others that have plagued smartphones since the dawn of the iPhone App Store.

Desktop Apps vs. Mobile Apps: Same Model, Different Tastes

Although smartphone app stores have given rise to small-footprint, single-use programs, developers aren't ready to write off desktop apps. The developers I spoke with believe that full-featured software is far from dead, and that it will continue to have its place in desktop app stores.

Bill Taylor, a product manager for voice-recognition software firm Nuance Communications, believes that the small scale and limited functions of smartphone apps are a byproduct of technical limitations, such as weak processors and low storage capacities on early handsets. More-capable devices, with more-powerful microprocessors and memory, he says, will lead to more-capable apps.

"I think it's going to make sense from a user standpoint to have a more seamless experience," Taylor says. Going in and out of five apps on your smartphone or tablet to accomplish one task, such as editing an image or updating a spreadsheet, just doesn't appear to be all that great of an experience, Taylor says.

So far, Taylor's instincts seem to be correct. On the Mac laptop and desktop, users are willing to pay more for great software. Among the top 100 Mac App Store applications, the average selling price is $22.54, according to market research firm Distimo. That's about $20 more than the average price for the top 100 iPhone apps. The Mac App Store is the desktop equivalent of the wildly popular App Store for iOS devices, which aims to simplify the way Mac users discover and purchase applications for their computers.

While the "freemium" business model has flourished on iOS, Mac developers selling their goods on the Mac App Store haven't embraced the freemium trend for sales. The term "freemium" is a bit of jargon that refers to a free app that entices you to fork over money to unlock more features through in-app purchases. Only 4 percent of the top-grossing Mac apps are freemium, versus 50 percent for mobile app stores.

Although app-store skeptics like to dismiss these stores as a place for silly diversions rather than serious desktop software, that stigma has more to do with the difference between phones and full-size PCs than with the app-store business model. On the iPhone, games are the dominant category, according to data from market researchers at Distimo and AppFigures. In the Mac App Store, however, utilities are the most popular, and productivity apps are among the top three categories (although, to be fair, so are games and entertainment apps). The data suggests that on desktop computers, fart apps and other time wasters aren't such a hot commodity.

'People Love Installing Software'

That's not to say that smaller, cheaper, single-use apps won't play a role in desktop app stores. But instead of cannibalizing larger apps, they may draw people away from the open Web.

Healy Jones, vice president of marketing for OfficeDrop, noticed this shift away from the Web immediately after his company released mobile and desktop apps for its document-scanning service.

OfficeDrop, which provides searchable cloud storage, says that it sees seven times more user engagement through its apps than it does through the Web browser, Jones notes. Since releasing its first apps in 2011, OfficeDrop's user base has grown from 7000 users to 140,000 users.

"We had a thesis that people did not want to install software; that the cloud meant that people could use a browser to interact with software and would never have to install anything. We were completely wrong," Jones says. "People love installing software."

Kevin Foreman, vice president of consumer and mobile applications for Inrix, wants to capitalize on the shift away from the Web. In the past, the company has licensed its traffic data to Web-based services such as MapQuest; but with Windows 8, Inrix will launch its first native app for desktops to help people avoid congestion before they get in the car.

Software Redux: The Web Is Out

"We used to live in a world of applications ... and the world told us all, stop downloading apps, because you can get viruses and stuff, and we all moved to the Web," Foreman says. "We've come full circle. Now we've moved back to an app-based world."

The difference now, Foreman says, is that the ecosystems are in the hands of a few key players--Apple, Google, and Microsoft--so app developers have a better chance to get discovered. Instead of focusing on search engine optimization, software makers must now think about app-store optimization to get themselves noticed.

I won't get into the debate over the merits of native apps versus the open Web. Plenty of ink has been spilled elsewhere on that topic. But given what developers have discovered firsthand, we may see users clamor for native desktop apps, where they previously deemed Web apps to be sufficient.

Next Page: At the Whim of the Gatekeeper

At the Whim of the Gatekeeper

Anyone who has kept up with Apple's history of banning iOS apps knows that app stores aren't hospitable for all developers. Software makers--and by extension, users--are at the whim of whoever controls the app store. For security or business reasons, these gatekeepers can place limits on the types of software available, and they can change the rules at any time.

Just ask any developer who is dealing with Apple's new sandboxing requirement, which as a security measure limits the system resources that apps may access. In the Mac App Store, some apps now lag behind their direct-download counterparts as developers work to include sandboxing and wait for Apple's approval.

"This most recent submission, we've had some issues, and that's because [Apple is] going toward a stricter process where they're sandboxing all their apps," says Arnstein Teigene, a product manager for the Opera Web browser, whose latest version has yet to receive Apple's approval. "And that becomes quite challenging for us to get all the different plug-ins to work, because we need to talk to third-party software."

Unlike with most mobile app stores, developers and their users have an alternative on the desktop: They can release their apps for direct download via the Internet, and bypass restrictive app stores entirely.

But going direct has its own drawbacks. Microsoft's Windows Store, for example, will be the only place for users to find Metro-style apps. Developers who skip the store won't be able to take advantage of Windows 8's unique features, such as side-by-side apps, universal in-app search, or the charms bar for sharing content. On the Mac, only software from the App Store will be able to use iCloud for syncing data between devices.

App Update Fatigue

With a centralized app store, users not only get a single source for app discovery and billing, but they also get a one-stop shop for app updates. Although this arrangement could cause some headaches if you have a few dozen apps to redownload, it also means fewer notifications popping up at startup or cluttering the taskbar, and potentially faster delivery of new features and bug fixes.

Kevin Foreman of Inrix says that he was surprised to learn how frequently users hit 'Update All' on their mobile devices instead of rebelling against so many updates. He now expects that trend to continue in desktop software, and he thinks users' willingness to update is largely about trust and convenience. "They know ... that it's approved by somebody, and it's not going to hurt them," he says, "so why not get the latest and greatest?"

OfficeDrop's Healy Jones is happy to bring more updates to desktop users, because new versions drive additional engagement. "The app stores let people know, 'Hey, that thing you tried a while ago has actually been improved,' and then it prompts you to go check it out again," he says. "So the strategy of releasing something and then improving it over time actually is a successful marketing strategy."

On desktops, though, some developers are accustomed to launching paid updates. Unfortunately, neither the Mac App Store nor the upcoming Windows Store has mechanisms in place for this. Developers who want to charge for a much-improved app will have to release a separate version of their software or sell additional features as in-app purchases.

Neither option is feasible in all cases, says Marc Edwards, director and lead designer for Bjango, which sells the popular iStat Menus outside the Mac App Store. "Version 2 often bears little resemblance to version 1," he notes. "If we wanted a major update to be an in-app purchase, we'd probably have to include two versions of the app in one. It's all a bit clumsy and doesn't fit with the way we work."

It comes back to the issue of gatekeepers. If developers want the wide distribution that app stores allow, they'll need to adapt their business plans to fit the app stores' rules. Edwards describes the app-store model as "brilliant," and expects future Mac products to be exclusive to Apple's App Store, where appropriate.

Not Another Stand-Alone Revolution

At its debut, the iPhone App Store rocked the tech industry because it made mobile software easier to acquire and more fun to use. It also took advantage of smartphone hardware--accelerometers, graphics processors, and cameras--in ways that Web apps could not. And because the App Store was the only way to download new iPhone software, it had an easier time becoming a phenomenon.

Desktop app stores won't have the same meteoric impact on how we consume software. The Mac App Store has been popular, but it hasn't fundamentally changed computing on its own, because many of its benefits--such as digital distribution and full access to device hardware--were already available elsewhere. Desktop app stores will merely add convenience in the form of centralized billing and distribution.

The next sea change in how we use software will come from online services, which will act as the glue that holds all of these new apps and platforms together. As Kevin Foreman of Inrix says, "In 2012, it's just me and my services. If you think about Netflix and Pandora, or even electricity, I don't really care where electricity comes from, I just want to plug my stuff in the wall and have it work."

Follow Jared on Twitter, Facebook, or Google+ for even more tech news and commentary.