Microsoft is quickly moving to a place where they are no longer a monopoly. Why would they want to force people out of their product? Once you force them out of Win XP, you take the change that they will move to Windows 7, OS X or Ubuntu Linux. At my school, they already have triple-boot machines, and one of them is Windows XP. The Linux side can surf the web, open PDF, edit files, and print to the lab's printer. OSX I would not know because I am not a mac fun, but Office can be used on OSX.
I thought pushing people out of WinXP was a good strategy 4 years ago when Microsoft looked stronger and there was no alternative. But today, I think they could be accelerating the inevitable.
Its as if Sony decided to make the PS2 obsolete in hopes that the user-base will move to the PS3... it could work, but it could also backfire.