People can debate the legality of the hit, but Lucic gets suspended because:
1. He is a repeat offender
2. It was deemed illegal in some way, otherwise no penalty would have been called
3. It was Ryan Miller, whom the NHL still uses as one of it's top faces of the game
4. It caused an injury
5. The hit has become a huge story. If the NHL is trying to reduce injuries/concussions, a message needs to be sent, and they need to show a commitment to that plan.