HN is not youtube, where there's no threading of comments and where it's impossible to divine who you're responding to without the @name.
Here it's quite obvious who you're responding to, because your comment is indented under the comment you've replied to.
Also, while we're at it, replies that say no more than "I agree" or "I disagree" are generally frowned on here, since they're almost completely contentless and don't contribute to the discussion.