I feel like online fandom used to be more about smaller, more specialized communities? (I don't know if the JetC community could flourish now quite like it did fifteen years ago.) LJ allowed for a really interesting mixing of people that maybe seemed less common in mailing list fandom?

This is totally anecdotal and based on a period of my life when my memory is pretty shaky, so I could also be remembering wrong? But I wouldn't be at all surprised if there was a connection between fandom migration to new platforms and changes in fannish culture.