It is not always easy, even possible, to learn from the airline the real cause of any delay. That is necessary to make any claim correctly. I've heard from various friends on more than one occasion that ATC or weather was given as the reason for a diversion and/or subsequent delay: one in the case where the return flight a/c never arrived but diverted before making an approach or holding. They were stuck for 3 days and told it was weather and not the fault of the airline. I'm not sure if the court case has finished as they later discovered this reason not to be correct. Correct information is vital and powerful.