Like the earlier post, I think the skipper is ultimately responsbile for all those on his/her boat, similar to an aircraft pilot.

Accidents happen, stuff breaks, weather turns sour, errors are made. Insurance is there to help provide that peace of mind knowing the skipper can "do the right thing" and take care of anyone or anything injured during prudent operation of the vessel.

As for the PRO responsibility, would you think that an America's Cup team would challenge (or sue) the PRO if they conducted a race beyond the design parameters of the boats in the race? I know there was an s* fight about the minimum windspeed...

The T-500 is more of an adventure race for those with a certain level of competency. Buoy racing, in my mind, is somewhat different in that those with little or no experience are welcome, and it is in that context that I feel the PRO should exercise a bit more discretion with respect to course set-up (not setting the gate width at 1 boatlength, minding the wind/sea conditions, etc.)

Personally, I can't think of any reason I'd sue a PRO, since it's my judgement to participate in the first place. But if I were pro- or semi-pro and this regatta somehow influenced my paycheck, I'd probably have a lot to say if the PRO was making bonehead decisions (like sending a single-handed fleet out in 25 kts, knowing most would break down/crash and the PRO doesn't have enough safety vessels. That would seem negligent on the PRO's part because of the potential for increased chance of accident/injury)
Yeah, and setting a buoy in less than 6" of water is funny to watch, but not funny to drag the boat across!

Oh, and those waivers are nice to have, but most of the time don't really work (look at BKs earlier post - note that was for commercial operations, and not non-profit or community stuff)