...and you can do any of those things on any OS. Look, I am not saying that there would be a drastic shift in the market but rather that the potential for a shift would be there. One of the biggest draws of Windows has always been that that's where the games were. If there aren't any games, then the only thing that Microsoft has is recognition as you allude to.
Either way, it's a gamble. Sure Microsoft might keep people buying Windows and Office at home and add a Xbox, but the incentive to keep Windows around won't be as strong and I could see a lot of people switching to a Mac. A majority? Probably not, but enough that it might not be a good idea for them to sabotage PC gaming at the expense of lost sales of Windows. Then again, I am sure they have guys working the numbers on all this stuff and maybe it'll drastically increase their profits even if they lose 20% of the home OS market. I'm just not so sure.
I think the problem is that MS knows that for a shift like that to happen, they'd have to make some drastic changes which really tick PC gamers off.
The reason why such a shift wouldn't occur is the same reason Cobra didn't buy a PS3 when his 360 died.
The problem is that we are too heavily invested in PC gaming....
From what I understand, developing DX games for another other OS is impossible/illegal, because MS owns DX, and while there was a time when DX and OpenGL were competitive, DX has blown much further ahead.
Then, it isn't like a console where you can just own two. Here you have to dual boot, and while guys like us wouldn't mind, the average gamer would find it too daunting.
The other issue is that to develop for another OS, a developer would have to take a massive risk, and I can't see anyone trying that aside from some big name publishers.
The final thing is WHY. Why would we want to shift. I mean, yes, MS is massively indifferent to gaming on the PC, but it is indifference, not sabotage.
Windows is still an open platform, so would it be worth the effort to go to another one?
By the way, I like a lot of ideas in this thread. It would have been interesting if MS had instead focused on making PC gaming.
Ren makes a few excellent points as well.
There is also no doubt that the launch of the Xbox 360 helped PC gaming to some degree. At least for the first two years of the 360's cycle there was a definite phase where where PC gaming got a boost because there was a sudden jump in technology which wouldn't have happened otherwise. Then you had a lot of development for the 360 of console style games which ended up being ported to the PC.
edit:
I'd also like to point something else out. Just look at how long it takes when there is a new OS (like Vista) for video card manufacturers and game developers to get their act together. In many ways Windows 7 is like Vista SP4. The point is that it takes the developers of the OS, the video card manufacturers and game developers many years just to get games performing at an acceptable level on a new OS. For the first few years XP was easily outperforming Vista in gaming... it is just a huge undertaking.
I think MS realizes all of this. They know that not one, but a few software giants would have to get together and put in a massive undertaking to make another platform a reasonable competitor to gaming on Windows.
And while there has been indifference, MS knows it shouldn't kill PC gaming all together. That's why they continue to release substantial updates to direct X.
Besides, all console development happens on Windows anyway.