This thread raises a related question that I've always had.  Why are campgrounds nearly universally a 72 hour cancellation policy or longer and you pay for the whole stay regardless if you leave early.  Standard hotel policy is 6pm day of arrival.  I'm seeing a little more 24-72 hour cancellation policies but you can still leave early.  This way when the flooding or train or whatever ruined the first day, you can roll out before check-out time and the spot is available for the next nights drop-in.  I think this plays in to the answer so many give on this site about not making reservations when traveling other than high demand areas like national parks, CA or OR coast, etc. I understand those having stricter policies, just as say Disney Resorts would.