I think the show is funny. I catch pieces of it every once in a while. You have to keep in mind Hef is his company. Playboy is supposed to be every man's fantasy. Huge house, wild parties, multiple women. Hef has to promote that fantasy, and those three help him with that. It seems more like a business relationship to me than a sexual relationship. More like, "When we're on TV and out in public, you act like my girlfriends. In private you can do what you want so long as it doesn't interfer with my company's image."
I read somewhere that the girls get $1,000 per week spending money. I bet that's really their salaries. They have no rent, no bills, he buys all of their food and the cars. It's not really such a bad deal especially if two of them aren't having pervy old man sex with him.