I stand to be corrected but my understanding of the EU rules are that you are entitled to compensation unless etc. etc.
I think that's how it works too, and the airline has to offer it, you don't have to demand it.
In other words it's up to the airline to show that circumstances were outside their control, not on you to prove it.
Why does that neccessarily follow, if it goes to court?
I also think the 'unless' has so much room for manouever that airlines will argue that they hardly ever have to pay out. Has anybody actually tried this in court? (The example above, if true, never made it to court)
(It's all in EC Regulation No 261/2004)