I guess it depends on the place, and who frequents it.
In this town, there isnt a lot to do except go to the bars. Its the "thing" to do here. Usually the groups come in and maybe one of the guys will be after something specific, the rest of the group just hangs out. The way I see it, its a peer pressure thing, at least at my age. Im just not the type of guy to go out looking for one nighters, but I end up getting dragged along with some buddies that are.
I dont think the bars are for one nighters as much as the clubs are. The bars here are more for relaxing and meeting friends, playing pool, and if you happen to catch someones eye, then whatever happens....
But the clubs are more about hooking up with someone. I mean, its not like you have meaningful discussions with that music going. You go in there with a purpose, and it obviously isnt to relax.
Just my observations here. We have 2 major and 1 minor college here in town, and the bar scene/clubs are the main off-campus focus.