I wonder. Considering it would be easy for HN maintainer to implement this feature I came to the conclusion they considered it and chose not to go with it. Maybe because that would somehow degrade the HN experience. Maybe that would shape a `quick-reply-on-the-spot' tendency instead of people getting back to the comments a few hours later to check out if the conversation brought new insights. A mean to keep some kind of posters from over posting.
The most addictive notification is "someone replied to you"... you want to see what it is, and then you often wind up replying.
So it will lead to more replies from people acting on impulse and arguing.
When you agree with something, you share it. When you disagree, you comment. So thus we can measure how popular and controversial something is by how many shares and comments it has (horizontal and vertical).
