I think she lets the omniscient be a very Harry-perspective voice. Thus, hexing Draco's gang is good, because what kid doesn't like winning a fight against their archenemies without a scratch?

I think she's also afraid of being thought too moralizing if she has too many non-school-imposed consequences for rule-breaking, that it will seem like "Maybe it was the right thing at the time and the world would have ended if he hadn't done it but it was still a bad thing to be doing."

I maintain that the Harry Potter books suffer from first series syndrome -- SS was the first book JKR had ever published, and she's trying to keep the rest of the books roughly within the parameters of the first.

God, I hope my first books don't make it half so big . . .