I do think in these "loophole" situations, it's down to the ethics of were the restaurant made aware of the loopholes / restrictions (unlikely) and was there a realistic expectation to be covered. Awfully difficult to verify, but in a case such as Katrina, there's a large number of similar claims and if they can find another company that has paid out despite a similar exclusion, then there's potential to push back against the insurer.
Insurance companies do get a hard press, sometimes fairly, sometimes unfairly. Sadly a few people see them as faceless & heartless big business (which some of them are!), but don't appreciate that paying out on a risk that wasn't covered means higher premiums for all in the future to recoup the loss. For an insight into a very public instance of ambiguous coverage, look no further than the WTC claim (which basically needed to decide was it one event or two).
Loss adjusting IMO requires a mindset totally different to most that work in the industry. It appears the key skill is a healthy degree of distrust and a keen understanding of not just what was covered, but what was not.
In this instance, there sounds like some grey area. Insurance companies can be challenged, though I'm assuming the owners took legal advice and were warned off pursuing such a course of action.
N.B. I used to work for three different insurance companies (I'm now in IT) in the actuarial field (aka the grey eminances!). My closest experience to this however was a personal claim when my flat was broken into.