I was under the impression that he was third on the depth chart now, and the redshirt quarterbacks this year would be ahead of him after Desormeaux leaves. If he would have indeed started his senior year, maybe he felt that he would be better off somewhere else anyway.
As for all of this moral courage stuff, you're putting all of your feelings of allegiance to this team on him. He was a pretty highly recruited guy and I would imagine he felt he was going to get his shot pretty quickly. In a perfect world where college sports are the end all to be all (hardly a perfect world to begin with), I would agree that he should have stuck it out. BUT, people transfer all the time. People quit mid-season all the time, and that's just life.
I'm just saying that the players aren't always as emotionally tied to the program as the fans. In fact, I'd imagine that most of the time the players aren't as emotionally tied to the program as the fans. The move does seem a bit like sour grapes, but c'est la vie.
If Desormeaux is the starter again next year, I doubt the program will miss a step anyway. By then one of the redshirt QBs should be ready to carry the load.