Thats exactly what I think. If it was all penis jokes, it would be stale after 1 episode. But there is relevance in their stories. Also, they do a good job of poking fun at dirty jokes (eek, a penis and the Bono is crap episodes) and show a good amount of irony in their own views.
My favorite example is when they did the chat roulette episode. “You gotta put up with a lot of d1ck5 before you find a real friend.”
That one was hysterical.
http://www.youtube.com/watch?v=4gNyDZmQyeY&feature=youtube_gdata_player
As demonstrated in the “Cartman Joins NAMBLA” episode, we all agree these perverts should be burned in hot oil.
But let’s at least get a good laugh at their expense first...
Guy jacking off.
Guy jackng off....
Penis....penis...penis