In any case, his "star power" is pretty much limited to politically interested conservatives -- and not all of them.
Rush is the number one talk show host in America, and has been for what - twenty or more years now? He's the leader of an entire industry, and that's a fact. It translates into dollars. Lots of them. It's the same sort of box office power that certain superstar entertainers have.
People at that level in the entertainment and media fields have mega clout in their industries, and no one pushes them around. They say what they want, and do what they want, because they can bring the money. No one's pulling Rush's strings.