The raft companys would argue that they are more experienced and capable than the private boaters, but the custies are more fragile, so it probably cancels out. I think most raft companies have their own internal policies about when to stop running certain sections, or when to restrict who is allowed to participate (or guide for that matter). It is up to the raft companies to make these decisions themselves and educate participants (and not run stuff if they are going to flip every single boat). Same goes for private boaters.
The problem with closing stuff is what makes something the "right" level to close it? If the chute at over 6ft is too dangerous to run, then would that make Gore Canyon illegal to run at all? The chute at 3ft is too dangerous for me in my kayak because I suck at kayaking. That's why I don't kayak Dowd Chute...
It takes a big man to cry...It takes an even bigger man to laugh at that man.