The corporate IT market runs in 10 year cycles. But only because they *can't* run in 20 year cycles. There is a reason why MS is still supporting XP after 10 years and will still be supporting Win7 past 2020.
As a rule, corporations use PCs as long as they still run (or the support contract does). For most companies, those are capital investments and part of overhead instead of profit-generators. Why do you think there is so much corporate whining over the Win8 GUI? They don't mind changes to the plumbing or incremental changes to the APIs but the GUI is what users see and any time they see "GUI changes" their beancounter minds see "retraining costs!" regardless of whether or not those GUI changes might result in more productivity or lower support costs.
You have to live in (and fight with) a corporate IT environment to appreciate how different it is from a true personal computing environment. After all, it's *their* computers and software, not yours...