Rush's style takes some time to get used to. His humor especially takes a while to grasp. His jokes always somehow manage to make a clever point, while at the same time torquing off everyone who doesn't take the time to understand or think it through (that would include lefties by default). As a result you get regular listeners who catch the full insight of the joke and think he's brilliant for it. You also get a whole lot of screaming loons who say he's an idiot or a bigot or whatever, because they get caught up in the surface meaning and never manage to see all the way through to the real point.
I think fistful is right. If you think one of Limbaugh's shticks is idiotic, chances are the joke's on you for not catching the man's real point.