Newspapers read the letters before they publish them, otherwise they'd be full of rude/obscene/complaining letters. Newspaper websites have moderators who read the letters and also have 'flag lists' so they can home in on known 'trouble makers'. Facebook open a channel that lets their users post content that is not seen by any Facebook staff before it appears on the website. That is the big and legally recognised difference.
Having said that, I'd reward users who flagged seriously damaging content with some kind of brownie point system. Maybe extra Farmville crops, or whatever. (I may have got that wrong, I don't use Facebook.)