I have a huge number of clients that are still actively using XP. The fact is, XP, for many people, is good enough. The only reason they're upgrading at all is purely due to attrition -- their old computer dies and they replace it with something running W7.
And this is ignoring my corporate clients, who are using software that is integral to their business, that hasn't been updated in years and does not run correctly on Windows 7.
The "always be upgrading" mentality in the computer industry is a serious problem for end-users.
But unlike the Windows upgrade cycle, this costs nothing.
Even though there are usually feature updates mixed in with the bug fixes and security issues, many people (especially non-techie people) lump the Chrome updates in with OS updates as a necessary part of maintenance like changing the oil in a car.
Upgrading Windows beyond XP currently adds very little of significance to most people though, particularly corporates with many many desktops to upgrade (and people to support when they do) and home users with limited cash.
From a designers point of view the "just upgrade already" argument can't wash. We can't force our users to upgrade there OS (we can only just get away with cajoling them into upgrading their browser or occasionally (but increasingly) choosing an alternative (though this is less of an option for corporates for the usual reasons).
The accusation is that MS is trying to make IE9 one of the reasons to upgrade (and therefore pay for that upgrade). This is the same accusation levelled at them with DX10 and later, and it is equally correct (and equally understandable from their commercial PoV). In the case of the browser though this is seen as more onerous because your internet access method is more ingrained in your life and much more potentially damaging when there are security issues.
A large client of hours (a major bank) is rolling out IE8 to their users (who are currently stuck on IE6) in a few months time. If IE9 had promised XP support they might have planned to roll that out instead, though a little delayed as they would need to wait for at least the RCs to start their main roll-out testing - so IE9 not being available on XP is definitely going to have an effect on the number of people still using the irritations that are IE6/7/8 in corporate environments.
And this is ignoring my corporate clients, who are using software that is integral to their business, that hasn't been updated in years and does not run correctly on Windows 7.
Not refuting the rest of your point, but Windows 7 comes with "XP mode". It's literally a virtual machine running Windows XP.
Saying something which works in Windows XP "doesn't work" in Windows 7 is obviously misguided or wrong.
And this is ignoring my corporate clients, who are using software that is integral to their business, that hasn't been updated in years and does not run correctly on Windows 7.
The "always be upgrading" mentality in the computer industry is a serious problem for end-users.