I think the main issue - in our situation at least (I mean personally) - is that if you as an Entertainer/Act invite people up on the floor either directly ("Come on everybody get up and dance!") or inferred (simply playing known, popular, dance music or styles of Dance) and someone falls on their ass, that person is entitled to sue whoever they can come after.

Could be (and most likely will be) the Venue.
Could be (and possibly might be) the Artist.

I want to be covered for the second possibility, and professionally, apparently, I HAVE to be.