It's not just true for projects, but also webforums.
When was the last time John Carmack posted on Slashdot? How many Ubuntu developers post on OMG Ubuntu? How much interesting posts is there left on Planet GNOME?
I believe the quality of content on any site depends not only on the participants and the technology used, but also on the policies and behavior (or as others say: censorship) enforced by the maintainers.
Reddit and Slashdot do it by letting users vote on posts, Planet GNOME does it by selecting the people that may write new posts (gnomememes? commit digest?), Facebook and Twitter make you maintain your own view on the posts. LWN so far only displays the status and id of the poster to give you an idea wether you're posting to someone "important".