You're right about that. It might be that I suffer from a "person B" problem :)

However I still think that the "short-lived" nature of discussions here is a relatively independent problem. I think integrating a way to "subscribe to a story" with email alerts on HN itself (rather than independent apps like hnreplies.com), and _displaying_ the number of people who did subscribe, would pave the way for longer-lived discussions. By seeing the number of people who did "subscribe to the story" you'd know whether or not it's still worth posting a comment even though it's been a day or two.

Maybe that's the reason forums have longer-lived discussions. You can easily get alerts when there are new posts in a discussion where you've posted.