A quarterbacks's success, far more than any other position, is determined by what team he plays for. Running backs, wide receivers, defensive backs, lineman, linebackers and even kickers are judged by their individual numbers - QBs on the other hand are judged primarily by wins and losses of the team.
I think that method is silly as QBs can only do their job and help it if their running game sucks or their defense is weak, but it is the system in which QBs are judged.
Like you said, Bradshaw made the big throws in the big games. During the year he didn't have to be that great as he did have a very strong supporting cast, but when he really had to step it up - he did.