Club or community?

After a good bit of discussion on the formation of online communities, it seems like we've agreed that the formation of some (if not many) of these communities are interest based. In some cases, like the ACL forums, deviation from the explicit topic may be hard to come by (excluding the occasional spam message). In others, like OrangePolitics some deviation is allowed, but while it is somewhat based on the political interests of the community, they are just that; one facet. Even when some deviation is allowed (or comes naturally... the origin really doesn't matter) there is an overwhelming gravitational pull of some special interest or topic that most groups seem to champion.
The idea of many of these so called communities leads me to think of their physical counterparts. I would be hard pressed to call the members of Jenny Craig or the African drum circle a community, yet in cyberspace, special interest groupings get that label. Are there different standards upon which we judge something to be a community? Or is the discourse simply different (e.g. there probably is more discussion in an african drum circle chatroom than an actual drum circle). What are the prerequisites for 'community' - and could they be applied uniformly to internet and physical groups? are these communities just online clubs?