Just a flying Mudcat visit before I head out to another festival..Well Lilith Fair was started partly to challenge an assumption that audiences would be bored by watching all female acts followed by all female acts when they aren't bored, apparently, by all male acts following after all male acts. I think it demonstrated that you could have women singing and playing all night and not be bored.
Sometimes I think that female singers are supposed to be better singers than their male counterparts but I don't have any concrete evidence to back this notion up. Part of the appeal of singers such as Alanis Morrisette is that they are deliberately not pleasant-sounding.
I'm trying to remember who was playing at the Milrace festival last weekend and I can only recall one band with mixed genders and they had a husband and wife couple in it. Often its impractical to take the kids on the road so somebody has to stay home with them and maybe stay-at-home spouses feel happier about long road trips when they know the band is all one gender.