I think you may be right about the ego. But both things may be right. If you have 3 World Series rings you've got 3 more than most players ever get, and what more is there to prove in SF? I can see moving on just to have a fresh challenge. And at his age I could see myself making the move for either of those reasons, or just because I liked clam chowder better than Cioppino. (though I don't)