Great thread Phil!
As far as I see it, salsa, more then any other dance really is a family atmosphere...but not just at the surface level. Once you're in, it is very warm, while if you are not, even if you're treated in a very friendly manner, it is still clear that you're not an "insider." I know that the last time I was in Toronto, it was very difficult to get any of the more experienced dancers to dance with me, since I was an “outsider” and, since only the less experienced dancers would dance with me, I wasn't being seen as an “unknown relative” by the more experienced dancers. Note, however, that in one's familiar haunts, familial membership is not proficiency based – this just tends to be the only calling card recognized when visiting other “families.”
There's also the fact that many "families" (especially these days) have very dysfunctional elements and dynamics as well...so there's definite “in-fighting" but, because its still a "family", everyone still comes together when faced with an outside "threat." For example, a couple of years ago there was a huge fight in San Diego about if salsa should be danced "on1" or "on2"...people were really getting angry and upset, and clear factions were forming. When it was suggested, however, that the dancers from "x" city were better dancers, well, that was pretty much the end of the division regarding timing (at least as a socially divisive issue).
I think there's also the more blatantly sensual (/sexual) dynamic of salsa, as well as the Latin cultural influence which all contribute as well…if one looks do be of Latino decent, one is more readily integrated into the family (regardless of dancing ability). Such a person is assumed to have cultural affinity to the scene and to understand that the sensuality and even blatant flirtation of the dancing is not (necessarily) indicative of anything off of the dance floor. Since such an assumption cannot be made about non-(appearing)-Latinos, they are less readily accepted, although, once accepted, are just as much of an “insider.”
I would guess that a similar dynamic is at least partially in play regarding the other dance forms you mention – the more body contact involved, the less (initially) friendly the setting…until one establishes one's “credentials.”
Anyway, just my take on it…