I believe that happens when HN suspects the account is from a person who was banned previously, based on IP's and/or some other heuristic. I've seen dang say something like "If you create new accounts to break the guidelines, eventually we just start banning your new accounts."
Perhaps! It might be that these people were unfortunate to share a network with someone malicious (maybe a university, or a company) and this dooms their initial comments.
