I also had the same experience with people in quake that I played with - I am sure if I caught up with some of the guys from the swedish QWCTF scene back in the day we would have a bunch of things to talk about, same with the community around the webgame Utopia.
I think it depends on how much time you put into the game and how engaged you are with it. Communities can develop around all types of games, but I agree that UO was a very engaging game and I still remember the people I played UO with 17 years later, even though I am not in touch with them anymore.