Windows 8 won't run on an ARM-powered devices, so as far as tablets are concerned you're talking about Windows RT.
"The difference is critical if you want something other than a toy that does email!"
I'm not sure where you get that idea from - Windows RT comes with Microsoft Office pre-installed, it has multiple language support, IE10, Xbox Live, Windows Defender, Exchange ActiveSync, and virtual private networking. It also has enhanced data protection using BitLocker technology. Windows update and Windows Defender are always running by default.
It doesn't have Windows Media Player, Windows Media Center, HomeGroup creation (you can join an existing HomeGroup but you can't create a new one), and you can't connect to your RT device from another PC using Remote Desktop.
An RT device is certainly much more than "a toy that does email"