For every 100 people who read HN, my guess is that 10 upvote stories and 1 comments. I bet that more than half of regular HN readers don't even know that the site is powered by voting despite the little arrows next to each story.
If people knew to upvote stories they liked on their own then the average story would have something like 800 upvotes. I agree with what you're saying because if everyone did this it would be really annoying, but certainly most people don't upvote the stories they like.
I up vote 1 in 20 stories because I only like 5% of what's posted to HN. Looking at new submissions is mostly a waste of time, but when I am board I will occasionally take a look. And I expect most regular HN readers act the same way.
Oh, I do not think the problem would be that the users are unaware of upvoting. Surely, about everyone (some excluded because everything is not always valid for everyone) would notice there's a clickable triangle next to the story title (Especially since there's just one(!)) - and most users should be coming from, or have visited another "social news board" with similar features previously.
Sometimes you simply do not like a story, article, linkpassing nearly enough to actually be thinking: "Hey, this was so interesting, that I am going to tell a really good friend about it - so he/she could enjoy it aswell!".
You bet half of the regular Hacker News readership does not know the frontpage is powered by voting.
I bet most of the fellow users have fairly or very high standards. Especially since there's so much quality content.
Just my two minutes of thinking and other eight minutes of editorial process. Cheers fellow reader.
If people knew to upvote stories they liked on their own then the average story would have something like 800 upvotes. I agree with what you're saying because if everyone did this it would be really annoying, but certainly most people don't upvote the stories they like.