More likely downvoted for not contributing to the discussion. While I'm sure it's appreciated, imagine comments like this being on top of the comment thread. I don't think anyone reading HN goes to the comments to scroll through a dozen of "Well done!" and "Congratulations!" comments before seeing comments with substance. It's probably safe to say people on this site go to the comments for extra information, insight and different perspectives on the topic.
I wish there were a way to share the voice of appreciation e.g. like that. Sometimes I really appreciate what a comment or submission had but I'm not sure how to express it. While up voting does that, it is anonymous to the receiving user, though on the other hand, I guess it's what keeps HN from becoming only about the 'likes'
I absolutely share the sentiment, but like you said, not having this feature is the sacrifice to make in return for a high(-ish) quality discussion board. The other end of this spectrum would be reddit, where you need [SERIOUS] tags and heavy moderation, and still get inside jokes, memes and circlejerking for the sake of karma/likes.
Well it was that or just assume that HN comments are only for bitching about minor discrepancies in the article, nerdy holy wars, or for general negativity.
Of course that's the general
impression outside HN so perhaps they're correct and I'm just fighting a lost cause.