can you imagine how much it would cost for a family with a couple of youngish children, on a flight of longer than an hour!! or if people refuse to pay, phew that wouldn't be a nice flight.
on a more serious note, their are people that are either on medication or for medical reasons have to access a toilet more regularly than most, and are unable to 'hold' themselves!
ohh and what if you don't have the correct change, will the stewardesses have change or may be a change machine, they could make more money put in a fiver and get 4 £1 coins out!!!!