Why not XP? The have no interest in supporting it. And millions of people still want to use it.
An open source XP would get many hackers interested in Windows, something they desperately need.
They are definitely making money on closed-source operating systems and operating system tools:
http://www.microsoft.com/investor/EarningsAndFinancials/Earn...
It wasn't free--it took a couple of hours of my time!