If anything, HN threads reward people who comment early. I’ve noticed the users with most karma are also extremely online and comment on a lot of threads early. If the thread becomes popular, their comments get more views and karma than someone who comments later. Even here, HN tries to mitigate this effect by giving every new comment in every thread and sub-thread a few minutes at the top when it’s new. This encourages people to comment even if they’re late to the party.
More could be done like removing the list of top users or moving profile karma a couple of clicks away, but HN does more than most websites to de-emphasise power users. That’s why I comment here and not elsewhere.