I think you may have hit on a key point for many dems. Unfortunately, it frequently isn't convicitions the Dean's of the world run on - it's only about getting the vote.
For example: When Lieberman ran the primary, he ran as a highly religious, orthodox jew, and he hoped to pull votes from that segment. And, he pressed for the pro-abortion votes. Ultimately, he was ex-communication from the jewish chruch and he lost votes in both segements.
Personally, I would rather see someone stick to one position rather than play the whole field. On the dem side, I've seen too much of the switch-hitting on issues and it has left me unsatisfied.