In our area (northeast US) there are some people who have house concerts quite regularly and others who do now and again. One series, running for years, has excellent performers and they also serve a terrific dinner, appetizers to dessert; the whole event (with two sets, usually around 50 minutes) runs well over three hours. I have no idea how the costs are covered, as the admission is low and goes to the performer. Mine are simple, I ask people to bring $X for the performer plus food or drink to share; I provide chairs, ice, cups and plates and such, and I host the performer if he is from away. You are right that many pretty big names enjoy a house concert between gigs when they are away from home, not only to pass the time and for a few extra dollars, but for the intimate atmosphere as well. Don't forget the desirability of local performers for house concerts, too. Often their fans wish they performed near home oftener, or in quieter environments. The regular listeners often know each other so it is a very homey atmosphere.