/* It does, as soon as your karma reaches 500 or something. A comment voted down sufficiently enough becomes "dead". But again, with sufficient karma you can vouch for a comment and resurrect it from the dead, thus preventing e.g. effects of a brigade attack. There are several more automatic preventive tools. HN is slightly less simple than it looks; maybe this is one of the secrets why it's still alive and relevant after 17 years online. */
Ah, that's pretty neat actually
It does, you don't have enough karma for it though. The threshold is/was 500.
It does, but I think it only appears after you reach a certain karma level.
It has, but not for newbies or people without a history of productive/popular comments.
Edit: interesting that this factoid attracted a downvote. It is factually true and doesn't indicate any personal opinion on the state of things.