It seems also that the majority of the time the penalty goes against the visiting team. The one exception that I can remember is one against Iowa last year when they were playing Northwestern at home, I believe, and one of the safeties for Iowa just laid out a Northwestern receiver right out in the open in front of the official.
I understand what they're trying to do with the helmet to helmet penalty being on the books.....but the implementation of it has been inconsistent, to say the least. Not only that, but many times when its called, the defender has led with his shoulder and the helmet contact is incidental to the intended tackling technique. This is what happened with LJ last year. He went low to try to tackle a player he was giving up about 40 pounds to, and that player tried to go low on him to shed the tackle. The result was helmet to helmet contact that was not intentional, and that one bad call was a turning point in the game because it nullified a fumble. The intent of the penalty is to protect defenseless players when they don't have time to react and brace for a hit. Moeaki was not defenseless on that play, he saw the defender coming and made a conscious decision to try to beat him to the lower position.
When does an offensive player get called for helmet to helmet contact? Lowering the helmet to try to break through for more yardage is a coached technique.