I was very surprised at the absence of Sinofsky at //build/ and everything else lately, and had the sneaking suspicion that things weren't going well for him ... Ballmer doing the demo was cool, but seemed like something Sinofsky would normally *love* to do, and to have that taken away from anyone else other than Ballmer would have definitely seemed off.
Anyways, I think Sinofsky made a lot of mistakes but really did a great job overall, and Windows 8 and Surface is a culmination of more than a decade of R&D and a solid vision of how the ecosystem should interoperate. It was hard to see, now it's easy to see that it will work out very nicely. Those of you who haven't tried Windows RT with a tablet or touch screen ... you're missing out ... believe me I wasn't too keen on it until I got ahold of a Surface RT.
I am inclined to believe Sinofsky when he says it's his choice, only because it is so soon after the launch of Windows 8 and Surface that I find it hard to imagine that Ballmer was so impatient and willing to stir things up at this time. Perhaps he decided he was going to move on because Ballmer isn't going to hand over the reins and he's finally accepted that. Maybe he's just tired of 23 years of trying to get people to do what he wants. Maybe he wants to leave on a high note.