I'm thinking that you may have been misunderstanding me all along. I'm not saying that *no one* except the diver has any responsibility. I'm saying that the diver is ultimately responsible for themselves. The diver should be able to make the right determinations of whether they can do a certain dive or not.
That said, I believe that dive operators should be doing what is necessary to ensure that they are not taking novice divers to dive sites that are beyond the diver's abilities. This is just good common sense and is in the best interest of the novice diver, the other divers on the dive and the dive operator.