It's actually a bit ironic. The "entertainers" tend to focus on extreams, which cater to a large percentage of the american public who are typically drones. I consider myself conservative (no, Darth, you are not the only one) and anyone who's gone toe-to-toe with me in a "heated" debate (they never really get heated around here - fortunately everyone respects each other's opinions enough) will attest.
Personally, I'm not a big fan of any of the political "humorists". Most of them think they are far more entertaining and/or enlightened than they really are and that just rubs me wrong, regardless of whether I agree with what they say. And for the record, I have agreed and disagreed with stances on both sides.
The irony is that the politicians themselves try to appear as centered as possible, while still taking a stand on certain "hot" issues. For example, I would be surprised if anyone who considers themselves "typically democrat, but..." would even consider voting for Rush. And yet the republican candidates frequently spin themselves to try to appeal to exactly those people. And vice versa...
The humorists have the advantage that they don't really care what people think of them. In fact, the more controversy, the more they are noticed.
And like Killer Joe says, the people that typically enjoy one or the other are more often than not zealots who are going to believe everything their favorite says and completely debunk what the counterpart says. Choose your truth...