If the comment is over 1 day old, you can't downvote it anymore. See, you can still downvote this comment on that thread because it's only 18 hours old. https://news.ycombinator.com/item?id=8081863

Ahh thank you, this makes perfect sense.

You can downvote? Does it come with higher karma?

There are downvotes and flags. People with at least 750(?) karma can downvote comments, so long as they are less than 24 hours old. No one can down vote submissions.

If a submission does not belong on HN you can flag it. Be cautious with flagging because you can (apparently) lose flagging privlidges. (I think I flag too many submissions and I have cut back on that. I think I flag comments carefully).

You can flag individual comments by clicking the [link] link which should then provide an option to flag.

There have been some discussions and guidance about the difference between downvoting and flagging but I can't find them at the moment. (But if you do get downvoted it's nice to remember that some people use it to express disagreement).

I can confirm personally that you can lose flagging privileges :)

My advice is not to flag off-topic posts and just stick to flagging spam or obscene content.

No, there is no story-downvoting feature on HN, at any level of karma.

I love how you can write this :)

https://news.ycombinator.com/leaders

I promise you from the bottom of my heart that I find that page embarrassing, even if I can easily rationalize why it says that.

There is no story downvoting. At a higher karma level you can downvote comments. It seems like it's not published anywhere what that number is, but you can figure it out easily enough by googling around.

For anyone interested, I got my downvote ability at 500 karma.

I suspect the threshold is >500, and that most people don't notice the difference between 500 and 501.

A better title would be "Why is down voting on comments disabled on some submissions?"