That's completely fair. Deposits should be ensuring that the dive op has revenue WHEN operating. If they decide to cancel, it doesn't matter if no one signed up that day, they were not making any income. And I would expect (someone like @Wookie can comment) that a business would base their pricing on number of days of operation, knowing they will at times get blown out.My beef is with dive charters that have no problem canceling a trip last minute simply because it isn't profitable while holding divers to a strict no-cancelation policy.
Even worse was once in Key West when I had scheduled two separate charters for my group of 6. 3 of us were doing the Vandenberg and 3 were doing a shallower reef trip. Late in the afternoon before the scheduled dive, the wreck dive was canceled due to not enough divers, no alternate dive charter was suggested, and worse yet, was that after I found a different charter for both groups, the first charter refused to cancel our shallower trip meaning we'd be forced to drive to 2 different marinas due to no fault of our own. I had to dispute the credit card charge to get my money back.
When in Florida, I'll be sure to look at the fine print and choose my charter accordingly.