This happens to everyone. Unfortunately, it's not a good enough excuse when, for example, the corporate sites I run go down.
No application, desktop or web app, is truly bulletproof.
Ok, but some are more than others. Facebook is not famous for its outages, as far as I know.
You are correct as far as I know. Interestingly enough most of the troubles I used to have were with the absurd amounts of JavaScript on their site and failed XHRs--no full outages.
But they do have a liberal deploy policy which is to deploy all the time and fix issues later. Has bitten them before, but generally considered a good policy.
Makes you feel happy you're not working at Facebook now :)