People suddenly saw all the ways to build relationships (not that that didn't happen via message boards, chat, IRC, etc.),

I see what you're saying, and it makes a lot of sense. Messageboards are a great way to meet people, but Livejournal tends to be more personal.

Again, not that the websites/etc. didn't allow for interaction, but it's harder to "drop-out" of LJ because you tend to invest more in it, personally.

Another good point - I have a messageboard I go to a lot, but rarely post at. I've gone months without posting, and weeks without visiting.