It's ALL ABOUT LIABILITY. That's it. Very simple. If all you had was OW cert and a diving accident happened at 61 feet, the dive operator could and would get sued, possibly forcing them out of business. Liability wavers are a joke. Definitely not worth it for them. Unfortunately, our country is a litigious state, and we must get used to it. One thing I will say, though, is that a good dive operator and/or DM will look at a diver's complete history before an "advanced level" dive, and should even accompany divers on an easy "warm up" dive beforehand to get a feel for how far along their skills really are, especially when that person is AOW with 8 dives under their belt. For example, on a recent trip to the Blue Hole in Belize, where you go down to the recreational dive limit, our group did 7 dives with the DM beforehand so that he could determine everyone's skill and safety level.