Whoa, I go out for the night and this thread has gone mad.
Can't speak for everyone, but when I was suggesting the old rave tunes, I was very careful to only pick very obvious tunes that would either be well-known outside of the harcore massive or would have characteristics that would appeal outside even if they weren't. They were then all confirmed by Droid, by all accounts an experienced DJ, as being tunes that do indeed go over well in a bar context.
As others have been saying, you have to remember that a lot of these tunes were in the charts, and generally it's become a cultural period that people have a lot of nostalgia for even if they didn't live through it. Obviously it's at least in part a British thing, and may not communicate so well elsewhere, but it's not fair to say these tunes will only appeal to a handful of obsessive ageing ravers. Also, no-one has been saying that all kinds of other music couldn't go down well in a bar. People were just talking about the ardcore for a while 'cause it was interesting.
The question of what sort of context/audience we all have in mind is an interesting one. Personally, as the original topic was phrased in terms of 'bars' rather than 'pubs' I was immediately put in mind of the somewhat faceless/generic bars you see all across town and city centres. These places quite often employ DJs, especially at weekends when they tend to open a bit later than your average pub, usually having them play popular stuff at a volume that people can still talk over. The clientele at these places is quite mixed; you might get a few people who in some form or other could be considered as trendy/scenester-ish, people who are musically hip and into checking all the options available, but the majority of the audience would probably be quite ordinary people. often working-class but interested in dressing up a bit and going somewhere nice for the weekend.
The downside, if you consider it thus, to such an audience would be that your selection would have to be quite populist, things with immediate impact and an overall fun vibe. The upside is that you wouldn't be tied to any one demographic, and therefore not to any one musical style either (compare this to clubs where even the most mainstream places will advertise nights as specialising in r & b, chart, house etc.). I see Slothrop has pretty much said all this better than me upthread, so I'm going to stop now.
EDIT: Big up padraig for the new subtitle, hahahahaha.