<_< That article is a good primer on copyright - but more for those who are seeking to know what one is and how to get one. I don't think it is too informative for those pickin' in public.
But that doesn't matter. The fact is that any place that plays music, either by radio, CD, live - whatever - should be licensed by ASCAP, BMI and SESAC. These licenses cover copyright use for performances at those places. In other words, you don't have to sweat it - unless you happen to record...and that is another thing, entirely. Some bands will also pay blanket licensing fees - for cover songs, again that doesn't include recording (recording requires a "mechanical right" license which is quite a different thing).
Of course, if its your own material, then the venue pays you for it (even if you play there for free) - if you are signed with ASCAP (or one of the others), and your stuff gets enough air time to earn a pittance or more of royalty!!
Andy