an uptime guarantee is important, in that it will form part of the contract you have with the web host. If your site goes offline for 12 hours without explanation you would have grounds to say that you relied on the guarantee when making the decision to purchase the hosting package, and although the hosting company may introduce all kinds of reasons why it's not liable it's better than nothing.
All other things being equal, go for a company that provides an uptime guarantee.
As mentioned above, any guarantee is only worth what it's worth but can be better than not having one.
The URL you referenced is incidentally a planted post for drawing traffic to a thin affiliate site, also available elsewhere such as click here and posted by the person who happens to own the affiliate site.
You have to careful what you read on the web, there's a rumour not everything is absolutely accurate:)
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