There is a lot more to being a good QB than just being able to throw the ball. There are plenty of QBs out there that have a cannon for an arm, but aren't star QBs or even good ones, let a lone a starter. Its whats between the ears that really separate the great from the good ones. Then, once in a generation, you get a guy like Tom Brady, who has the arm, pedigree and brains to succeed. I'd much rather have a guy with an average arm that has a great grasp on the game.