You're assuming that the primaries and caucuses are mere formalities at this point. They're not. The only places where Dean is really getting blowout numbers is in New Hampshire. He's only in first within the margin of error in Iowa. Nationwide he's only getting 15% support and is tied with The Weasel.
ANYTHING can still happen in this clusterf*ck (®John Kerry). Gephardt still stands an excellent chance of winning Iowa. Any sort of weirdness could happen in South Carolina. Dean could simply peak too early (it's over two months before the first primary). Remember: In 2002, a guy named Bill Clinton barely even registered in Iowa, getting only 3%, and lost big time in New Hampshire to that powerhouse Paul Tsongas. Only after those humiliating defeats did The War Room get their act together and start racking up wins in state after state.
Those other candidates still want to win, especially Lieberman, Gephardt, Clark and Kerry. They're not going to roll over for Dean. They're going to fight, and fight mean.
If Hillary endorses Dean before Iowa, I'll be convinced that he really was their guy all along. Remember, his big issue was originally going to be health care, with a plan which was very much similar to Hillarycare.