Sarah Jessica Parker and Julia Roberts are special cases imo.
Sure there are plenty of ugly famous people, but most of them aren't famous for their attractive looks. They are famous for another quality.
Parker and Roberts (used to) get cast in "sexy" roles though. They are supposed to be the eye candy yet look hideous.
Julia Roberts isn't great, but she is hardly in league with SJP. JR isn't what I'd call sexy but I don't think she is ugly either. Sort of like a rat. They aren't animals you want to hug but they have a certain charm or cuteness to them.