There's a huge non-sequitur there. You're assuming that people who aren't getting notified of their replies are thinking about what they're going to say on the topic. I don't think that's true. You see the reply to your comment, then you start thinking, then you reply to it. The time from seeing the comment to writing the reply doesn't change with getting notified or not.

> You're assuming that people who aren't getting notified of their replies are thinking about what they're going to say on the topic

No, i'm not assuming this.

For example one difference is that situation #1 is a surprise (you get a notification while you were in the middle of something else) and situation #2 is not (it's anticipated, you decide to check the HN website and decide to check for replies to your comments).

Situation #1 generates a startle reflex in some manner, whereas the anticipated visit #2 does not.

I think this really is the focus of it.

This is also the big reason there is an increasing delay on nested replies as you go to deeper. It forces you to calm down and think a bit more before coming back with an emotional reply instead of a thoughtful one.