But science fiction has never had much to do with science; science was just the trappings of the story.
I agree that the Internet has replaced conventions as the place where SF fans meet. The problem is not just that book readers find comrades online, but that there are fewer people reading books. Again, the people who, back in the 60s, would be reading SF books are more likely to be gaming, or into anime. People are just more visually oriented.
The “We’re not fans; we just read the stuff” contingent was always there, and only a small percentage of SF readers went to cons at all. I never did; my first con was in 1979, when I was 27, and I didn’t go again for another five years (when I was published and started attending regularly). I can’t see why the ratio of those who go to cons to those who read SF would have changed drastically
Fandom is going to evolve and be more and more an online community, with a handful of successful conventions a year. You’ll have a Worldcon, and World Fantasy, and major regionals like Boskone, Lunacon, and Westercon, but the small conventions are going to struggle. We made money in the early years of Albacon, but we lost our cushion in one year two years ago, when we moved to another hotel (and there were no cheaper choices). When I ran it last year, we were buying rooms at the last minute to meet our room-night quota. This despite being well-regarded, with a massively popular Guest of Honor (Terry Brooks – not my cup of tea, but if sales meant anything, he should have drawn the casual fans) and an excellent facility. We did a little better this year, and should be in very good shape for 2008, but it boils down to one or two planning errors and we’d be out of business. We have tried all sorts of things to draw people in – gaming, anime, webcomics, etc. – but our attendance remains stagnant with a core group coming every year and a few people showing up once and never returning. People who show up and who return are few and far between, and are usually made up of authors who had a good time and long-time fans who decided to give us a try and liked it.
Cost is a big problem: hotels used to be willing to cut a convention a break, since they didn’t get much weekend convention bookings, especially for holiday weekends. But now they can fill rooms and SF cons are at a disadvantage. Memberships are around $50 and increases are difficult, since people are paying their own way. That contrasts to a business convention that can charge $400 to join, and will get it since most people are on expense accounts. Since the business convention pays more, it gets priority.
So the economics are dismal.