Like Martin I'm interested in the situation that would merit 'moderation' (I use the commas because in my mind you are talking about censorship), in my experience it really helps a course if students think of the forums as their space, they help each other more and are more likely to share their thoughts, communication is the essence of what makes a course great and 'moderation' would very probably get in the way.
I think I have a situation where moderation may play a role. I am a Computer Science University teacher. We are considering using moodle as a support tool for undergraduate (say, 20 year old) students. I guess one can consider them as adults, and bullying or a bad attitude is not our problem at all.
What I am concerned about is students discussing assignements (which I am happy they do!) and then, unpurposedly, giving more information about what they thought or did than what they were supposed to -- those are personal assignments.
We have been used mailing lists for the discussion so far and maybe I had to stop 1 out of 100 messages (maybe less) from passing through. In all cases telling the student to rephrase her/his comment or to reveal less details of how she/he is approaching the problem has been enough. I suppose that this kind of moderation (call it "supervision" if you want) is not against moodle's teaching philosophy.
On the other hand, producing software with more capabilities that users can make use of "at their own risk" and following their own criteria should be, in the general case, positive. Not including a feature which is in itself not dangerous and technically compatible with the rest of the software is a form of "moderation" regarding what moodle users can or cannot do - just the opposite of what I have read to support the lack of moderation, only that applied to another level.