"why so few people vote or take part in the discussions."

To vote or participate you have to be logged in.

Would be interesting if PG released some data on logged in visitors.

Also, isn't the amount of votes the amount of net votes? So you could have 100 upvotes and 60 downvotes to net 40? (Of course that still doesn't jive with his numbers which I agree were very interesting and unexpected I would have never guessed that.)

Not participating could be also a) a confidence issue or b) lack of ability to type or use of a particular keyboard (I never comment from mobile for example).

Still, it doesn't explain the discrepancy in the numbers.

I don't know about the reason behind low number of votes, but the relatively low number of comments could be because the general attitude on HN (for the most part) is to be silent unless you have something constructive to say :)

For example, I don't know anything about python for example, so anything I can possibly say would be completely un-constructive (except if it's a question), so I shut my mouth and don't say anything; even when I see a (provocative) comment saying Node.js, which I really like, is shit and we should all be using python.

I've done my share of posting useless things on this site, but in the paste few months I've tried to not waste other people's times with useless comments and have removed maybe 40 comments (I would write a comment, read it and see it's not important and don't press "reply").

"to be silent unless you have something constructive to say"

Interesting. I tend to read much more stuff that I find interesting and have something to say rather than stuff I know nothing about.

"removed maybe 40 comments "

I don't think I've ever done that. If I get moved enough to comment I feel what I've said is important enough and the only thing I don't like is a downvote w/o explanation which is inevitable.. Actually it's the thing that I find fun and addictive about HN. I can usually predict downvotes as well on things that I say.

Would be nice if there was a way to post (w/o logging out) anonymously from time to time. Say once someone gets to a certain karma level they have the ability to say what they really think w/o fear of downvotes which I believe does supress what people think.

And in general, there is a reply that say what you think better than you could express yourself ;)

My hypothesis is that the majority visit HN to learn from those that do participate. Of course, their learning would be most effective if they participated themselves.