I've run an online community since 2001 and I've yet to meet the boogeymen of self-hosting. A small site and forum with ~100 users doesn't cost a shit to run ($5 per month, the cost of a coke and a sandwich where I live), updates itself automatically via CPanel, and it isn't much of an issue if it goes down for an hour or two every other year. That's an acceptable cost for not having to submit to anyone's whims about allowed content, and for not having to tolerate "redesigns". Twitter is probably down more than a standard Apache server.