Dennis
To understand fully the "exhibition" concept, you must first remember a few salient points about the UK.
Firstly, houses, especially the more modern ones, are usually very much smaller in the UK than America or Australia. (probably smaller than most Western countries I imagine). This means that small layouts are very common, most larger layouts being either in lofts or in railway modelling clubs. This explains why "open house" days are not common with domestic layouts (no room for viewing, not big enough to interest many visitors)
Secondly, the club scene.
Quite a lot of clubs in the UK, most counties (much smaller version of your states) having a choice of clubs within a ten to fifteen mile radius. However, many clubs are housed in multi-purpose buildings, being housed in one room of a community centre, a church hall, a local leisure centre/school complex or some similar building. Many clubs I know do build large layouts, but don't have the facility to erect the complete layout because of lack of space, or even have to disassemble and store the layout after each club night Some clubs are more fortunate and have permanent space big enough to house a large layout which is always assembled, but these are in a significant minority. There is therefore a situation where there are a few "club open days", but these are usually annual events, with a wide geographic spread.
Thirdly the Exhibition scene.
Because of the constraints listed above, it has become the norm to have exhibitions of all sizes and in all parts of the country. These vary from large, annual events like Warley (in the national exhibition centre) where there will be as many as 75 layouts and 120 trade stands, to small local events where there may be as few as six or eight layouts and one or two local traders.
Usually run by the local club, these events may be annual, twice yearly or even quarterly. There is invariably an admission charge which hopefully covers the cost of staging the event, plus a small surplus to help run the club concerned and improve the services offered to its members.
"The Exhibition" therefore becomes a social event for the members and guest layouts attending, a meeting place for modellers who visit, as well as a way of introducing the hobby to members of the public who "come to see the trains" As previously stated, the competition element is of little importance, but there is pride taken in the quality and accuracy of the modelling.
Wash it all down with a cup of tea and the consensus of opinion states that "a good day was had by all".
Hope between DS239 and myself some understanding of the mind set is emerging, if our quaint little ways are becoming a little clearer, glad to be of help!!!