This piece has an extensive quote from Reed Hastings as a departing Microsoft board member about Microsoft's thinking behind the odd way Windows 8 is organized.
They think there's a transition to touch taking place that's analogous to the transition to the mouse in the 80s and 90s. So they're putting the windows part of Windows into a compatibility box, the way they put DOS inside a window on Windows. You can still get to your Windows apps, but they're betting you will prefer to use the touch-based apps. That don't yet exist. But will soon. That's their bet.
My opinion: Wow. Why bet the company's user base and cash cow on that when they could just switch to Mac, as I'm sure a lot of them already want to, and get a "traditional" desktop.
Apple has been edging up to the same idea, in a much more conservative and rational way, imho. Testing the theory before betting what is not their biggest revenue source (Apple is now a devices company, iPad and iPhones make up most of their revenue). If Apple is being conservative, Ballmer thinks, I'll make the big bet. And hope I'm not wrong.
Problem is this -- desktop computers as touch devices is not a new idea. HP's first PC, in 1983, was touch-based. It failed. Not because there was no software, there was. The reason is that it's really painful to hold up your arm and touch the screen as a way of controlling the computer when the screen is vertical, not horizontal. The keyboard won.
Touch belongs in a tablet interface, for sure. But desktop computers need a pointing device like a mouse. I think Apple realizes that now, and isn't pushing the Mac in that direction. But this appears to be a bet-the-cash-cow move for Microsoft. Let's hope they have a Plan B ready to go!
See also: Jakob Nielsen's report on Windows 8.