True, but Manning isn't just any other player. He's cemented himself into one of the greatest players to ever play the game, and if he feels as if he still has some left in the tank, he'll want to remove all doubt and put himself ahead of the other immortal greats.
I don't think it's about the money either, I think it's about his legacy. Put Manning on the Bills, and they're a lock to make the playoffs. He's that good.