I would wager that a good 70-80% of people ages 18-25 watch those shows weekly, and the shows really do a good job of selling and advertising the democratic party in a humorous way. I can't remember who said it, but I once heard someone say that those two men are the two biggest reasons why Obama won the young vote so heavily. In this respect, I wonder how Colbert's exit will sit over with dem strategists.
You must not have a very diverse set of friends.
Kids who watch the show are already more politically aware than their peers who don't.
People who don't start caring about politics until they're 30 or 35 are Republicans while people who start caring when they're 16 or 17 are Democrats or hackish Republicans.