Quarterbacks might work the balls before the games as in maybe scuffing the balls up a bit. They might get a feel for it and press the ball into the ground perhaps like kickers do before they kickoff. Throw the ball and get a feel for it. But to deflate it, after the NFL officials inspected it before the game, to the levels that Brady and the Patriots did is called cheating and it should be considered as such by the league.
We are not talking about just breaking the ball in here, which I'm sure all teams and quarterbacks do. Someone probably took a needle to the ball and deflated it to Brady's liking and there has been accusations about this from the Colts months ago. The Ravens also have made accusations against them about this. The NFL has rules as to what the ball is supposed to be inflated to and these balls fell well short of the ranges that were allowed in the rules. You can't automatically say that this is a league wide phenomenon. If it were, this issue would have already reared it's head with multiple teams and would have been dealt with by now.
How many other teams have accusations of doing this against them? None!
The Patriots have disgraced the game and this isn't the first time. Unfortunately, we still have many people that try and justify it and that's exactly why they'll get away with crap like this.
Read what Troy Aikman thinks about this. He pretty much hits the nail on the head.