@Sunny
Tabletop is different. Even MMO guild stuff is different. In the first, you know those people and probably have known them before sitting down to play a game. With a MMO guild, it's smaller, more intimate, and you inevitably end up just being more social with those people, probably because a lot of MMO gameplay requires coordinating a bunch of people and trusting each role to know what they're doing. I don't think either maps completely to a MU* environment.
It's not too difficult a mindset. I mean it in the best possible sense when I say that I literally do not care about the player behind the monitor, nor their history anywhere else. Can you RP well, are you fluent in English, are you able to create interesting storylines, and not derail scenes to complain about whatever IRL bugbear has your attention of late? It's all I look for. It's no different to any other sort of hobby activity (hiking, bird watching, martial arts, whatever) where, sure, you'll get along with the people there, but you're there for another reason and, ultimately, you could replace any of those people with anyone else.
Of course, if those activity partners are people you get along with, then they'll become friends.
Hell, if MU*ers were replaced a fancy algorithm that could create poses I find suitable, that'd be enough for me. But that'd require some incredibly advanced tech.
This may be colored by the fact that my evenings, when I'm most likely to be sit down and devote time to a MU, the places are most likely to be virtually dead. If I needed to make social connections as part of my game plan, I'd simply be unable to.
@surreality basically sums up my thoughts, too. I have people on my Steam that I've met through MU*s but that's literally three people over a long, long time.