My experiences have been more with business than academics--and more international than USA. What the users have had in common that is so painfully missing here is what is called "Netequitte": rules for engagement on discussion threads.
Another difference is that materials and objectives are often highly structured--but not always.
I also participate in Sports blog discussion sites that are strikingly different from each other--even though they are all moderated similarly. Some are wildly confrontational and others are conversational and differential.
Online discussion is an art--and we don't have too many artists at GHMB.