The Fox Republican "debate" was somewhat surprising in that, aside from the expected ill-treatment of Ron Paul, they also ripped Romney for his past remarks, already retracted and apologized for, and didn't give the any of the others a clear win. I suspect that the tactics are still evolving on the best way to dispose of Dr. Paul. (full disclosure - I love conspiracy theories, but only for speculative exercise). In one of the previous debates, I first thought ABC made a mistake by giving RP as much rope as they did in the "debate" with Stephanopolos, but I came to think that they were allowing him to make the other Republicans look bad, which he did. If they had completely ignored him which I had assumed they would do, it would have allowed the others to coast on their strengths while ignoring the war.
I think Fox is doing something similar. I also noticed them dumping on Romney, but I felt they were also letting Guiliani and McCain hoist themselves with their respective prissy and robot personnae. They(Rudy McRomney) got the word not to shoot down at RP and leave it to the other dwarves to handle him. I'm surprised that the hit man wasn't Duncan Hunter, but he probably doesn't have the mental horsepower to go toe-to-toe with Paul, ditto Tancredo. The mini-debate was also a big surprise to me, especially on Fox, because, as you noted, they can just leave the slime to the moderators.
Bottom line, Fox is also trying to weaken the Republican side, for Fred (who I think will be the designated loser [think Bob Dole] in the general election to Hillary), or ultimately, for Hillary, when the neocons jump the Republican ship. Here's why I love conspiracies; Fred has lymphoma, so his VP will be important - they can get someone smart to balance Fred, in which case they can keep their war going for at least 4 more years, or worst case Hillary wins and they can keep their war going indefinitely.
So far, they've all underestimated Dr. Paul, I hope they have underestimated the People as badly.