Roobarb
I too am distressed that our country seems to cope so poorly with the vagaries of our weather. However as you point out it is hard to justify the level of investment required to keep our southern airports running in the event of severe snow fall, since it is an extremely rare event. There is a limit to how much any airline or indeed airport can spend to cope with all eventualities. For example technical problems resulting in an AOG are much more common than snow, however airlines do not always keep a spare airplane handy, or indeed sometimes even the spare parts to resolve such a situation immediately. Guess that we have to accept that no one has a bottomless pit of money and that there will be some occasions, snowfall included where passengers and airlines staff just have to accept that things cannot run smoothly 100% of the time.
As for leafs on the line well that is a completely different matter since it happens every autumn and for a prolonged period of time!