As much money as Win 7 is bringing in, I honestly don't see the need for a new Windows yet, but the folks at MS seem to think so. There's a steady flow of cash pouring in, plus a new Office coming, why screw it up? BTW, Office 2012 hasn't even hit the stores yet, and Office 15 is already in the works?
http://www.office-2012.com/tag/office/
MS won't really make that much more cash, it'll only divert from Win 7/Office 2010 sales. There's only so many customers to go around.
I do understand that tablet computers & touchscreens have popularity with some, it would seem that Win 7 could be modified for these things, just as they did with XP. There were both tablet & media center editions of that OS, the same could be done with 7.
Cat