Nothing's banned at the session I attend. Folks will simply find somewhere to wander off to while the repeat stuff is being sung/played. There's a tendency to play the same tunes every week, sometimes twice in one night if a player shows up late and starts it again.

Our youngest player brings in new tunes, and has the guts to keep playing them every week until people don't have a choice but learn them. I try to learn the tunes he does because I think my putting out the effort sort of hints that others can do the same. It's hard to get a bunch of old farts (myself included) to learn new tunes.