common law. bars are responsible for their customers (stupid, just like blaming the gun in a suicide) until they are sober. this was a huge issue that caused a lot of aggravation when i was bartending at a hotel, people would complain that i should be able to serve them until they were absolutely smashed because they were staying there. i had to explain, on numerous occasions (as i cut them off), that if they injured themselves, i faced the possibility of being held resposible.
what i find unsual about this case is not that they are being charged, but that its the state that's going after them. usually this is something that the victim or their family would pursue in civil suit.
I was a volunteer serving beer at Oysterfest, a giantic drink and drown for collegiates sponsored by alumni. I had to tell one girl I was not willing to pay $1000 fine for serving a minor. This was after she claimed to have no ID other than her empty beer cup! ;o)
I told her to go back to the same place for her refill. Never had trouble with the guys.