The rules are very arbitrarily enforced. If your one of the favorite, money generating teams then you get calls other teams won't get and don't get called on penalties other teams do. Look at the Pats Steelers game today. Steelers on red zone, throw a TD pass but the Pats defender grabs the receiver by the back of his jersey and drags him down, resulting in the ball being popped up and the Pats intercepting to win the game. The Steelers get a lot of favorable calls when playing other teams but in this case they were playing a more popular team so there was no call.
