The comparison is a group whose aim is not socialising in itself, but something else. In that sense I think it does compare. Particularly the Wikipedia of 2004-2005, when meeting other Wikipedians just started taking off. Though meeting up in 2011 is still going great guns and proving very productive.

I see from your comment that you were thinking entirely in terms of on-site possibilities. Have you been to either a Wikipedia or LessWrong meetup? Having been to both, I think the social aspects of a not inherently social site invoked by them are highly comparable.