How do you know that Forstall was the person advocating a yearly OS upgrade cycle? It seems just as likely to me that this rigid schedule was forced onto him and he couldn't deliver. Things like OS X Lion (a huge change under the hood) and the Maps places database just aren't things that can be built to a deadline.
Well, a mess was shipped and he was the guy in charge. So I'm assuming he was the guy responsible. If a mess really was forced upon him he should have resigned instead of sticking around to ship the mess.
I have in that exact same situation, "This will not be associated with me, I'm out"