It depends - I agree with this guy: http://www.moneysavingexpert.com/travel/flight-delays#martinsview
The law behind this is clear cut, the ethics far less so. My usual focus for these type of issues is on reclaiming – asking for money back that was wrongly taken from you. This, however, is...
That doesn't sound right. Suggest you have a look at this: http://www.moneysavingexpert.com/travel/flight-delays
Haven't read it all in depth, but it does say:
"Compensation for delays is only due on flights arriving over three hours or more late. How long the delay is determines how much you...