[Dove]

Actually, it's time-related and everyone sees it. Deeper comment threads have a timer that prevents comments for several minutes. It's to give people arguing with each other time to cool off.

[agumonkey]

Are those rules written somewhere ? I like the tree pruning effect of this one

[Dove]

http://ycombinator.com/newsfaq.html has some of them, but not nearly all of them.