I certainly wonder why the Democrats haven't replaced Governor Dean, but I am enjoying it while it lasts.
I think it's because Dean agreed not to run for President in 2008 if he had this job. He'd be more of a detriment in the Dem primary than he would be in this job.
My guess is that they won't replace him until sometime in 2007, when it's too late for him to start a campaign, and still early enough for the voters to forget about him.