the only way to get people off XP is to start writing applications that don't support XP.
Right now volume licenses for Windows 7 just aren't that appealing cost-wise, especially when you consider that XP does still work. Home users have a similar dilemma: they can continue to use Windows XP for browsing the web and playing Farmville or they can spend $120 on a neutered Windows 7 Home Premium upgrade.
That's too much money for what is perceived to not be that much better. I think you'd see greater, faster adoption with a lower cost and one version (just Windows 8, not Windows 8 Starter, Home Premium, Professional and Ultimate) that has volume licensing for businesses.
Microsoft has invested billions in Vista and Windows 7.
It's time to upgrade
Non-sequiter.You can buy support for legacy versions of VMS, Unix and OS/2.
Supporting all the legacy costs Microsoft money that
can be better spent on future enhancements.
It would be definitely be cost-effective to sell Windows XP support.The reason for withdrawing XP support are strategic, not cost-oriented (nor customer-oriented!!)