That should never be an issue. If the weather isn't good enough, then that's it. That's the pilots perogative and any club or school that kicks up a fuss about that is a poor one.
My problem is with serial last minute cancellers. Stuff happens and the odd time is rarely a problem, but when a pattern starts forming or people start ringing up and just canning the slot because they got drunk the night before, then that is unacceptable.
As per usual, there has to be a bit of give and take, but some people really do take the pi**.