Brian's right that the blame for these crummy debates doesn't rest entirely with the moderators. If Hillary Clinton and Barack Obama wanted to have a one-on-one, Lincoln-Douglas style showdown, I'm pretty sure they could get C-SPAN, and even CNN, to cover it on their terms. Put the thing on YouTube afterwards and they'd be set.
So, clearly, some of the candidates, generally the frontrunner types, believe these moderated, tightly-controlled forums help them. And they're probably right. One of the main lines of commentary on yesterday's showdown was that the narrative heralding Hillary's return was hollow given that she'd never really fallen. And that's correct. The nature of these forums doesn't allow anyone to slip up too bad. They don't have enough time to do so, and the other candidates aren't able to jump in and force errors. If better debates were desired, they could surely be negotiated. But they're not. They're not in the journalist's interest, and the relevant candidates don't appear to think they're in their interest, either.