While I suppose you're correct in saying it's easier to leave fandom then it is to up and move away, just living somewhere doesn't make you part of the community. Living in that area, going to the library and the coffee shops is like being a lurker in fandom. When you start to form connections, it's like meeting people in fandom.
Anyway, it's my opinion that rl and online community is of the same weight, but I grew up with the internet and fandom to some extent. Moreover, I try to be the same person in both RL and online. I don't know that everyone cares to.