Ya, I thought about after I wrote it. Though I believe you can only downvote comments not stories on HN.

You flag posts and they'll drop in the rankings, sometimes right off the front page.

i think the distinction in UX is important

downvote sounds like the opposite of upvote

flagging sounds like a reporting mechanism

they actually do the same thing, but they give totally different impressions to new users.

There is another state: vote-banned, like me; basically you see the up/down arrows in every comment but they do nothing at all (upvoting submissions do works).