You guys really are oblivious. Why stop there? Why not port Win32 over to Mac OS X?
Microsoft WANTS you to stay on their platform. If they start porting all their libraries over to other systems the whole reason for staying on Windows falls apart.
One of the biggest reasons for staying on the Windows platform, is the Office Suite, which already does run on the Mac platform. To manage this, then I imagine that large chunks of the hard stuff must've been ported already (they must've had a Visual Basic
engine for example. just to run the macro scripts).
No, what Microsoft wants to do, is leverage hard cash from Windows technology, whether you run Windows or not. This is why they took to stop fighting Linux, and just take a cut from the Windows intellectual property it used (allegedly).
MS already makes money from Office on the Mac, and they do that without flogging a Windows license. They will make more money with the Mac through virtualization.
So I don't think a full blown .NET implementation is that far off the cards.