I totally disagree. I see no reason at all, unless you're planning legal action, to partition the responsibiilty. The goal is a safe dive experience. That means everyone should be doing it right, making the right decisions, doing their jobs, and using common sense. In short, and for the purposes of creating safe divers, everyone who bears even the slightest responsibility for the accident bears 100% responsibility. If any one of the above parties had done their job fully, then the accident probably doesn't happen.
If anything, the real question is how to get new divers to understand this. They need to be aware that everyone makes mistakes. They need to understand that there are no diving angels who will be able to follow them wherever they might go and haul them out should a problam arise. They need to understand that, no matter where the blame can be partitioned, that 100% of the cost of the accident falls on the victim.
-bob