Maybe the posters might have deleted the comments themselves?
replyI often post comments on HN, just to delete them 5 minutes later when I realize I don’t care to deal with the replies I’ll eventually get.
You have to be quick because if someone does reply, you can no longer delete your message.
One benefit of this forum is that they purposely passed over notifications precisely to save us from the temptation to "deal with" replies.
replyI didn't realise messages even had a delete button. I'm going to reply here so I can check.
replyedit: you're right, there's a delete button.