It seems to be a UK thing, in the USA its almost completely the opposite I have found, possibly because flying is more accessible over there.
It seems to be worst at smaller airfields, where they still have that mentality that they don't really like 'visitors', they just like their own circle. Thankfully I have never experienced it personally, but I have seen it go on first hand to other people.
Its not just flying though, this type of thing goes on at golf clubs, tennis clubs and all other 'rich' associated pastimes. It is strange, but unfortunately I don't think that sort of attitude is going to change, particularly in GA.