There are many factors that could contribute to a power law for karma distribution. One conjecture is that other users tend to "trust" high-karma users and therefore tend to upvote their comments just because they have high karma.
Another is that high-karma users receive gratification from using HN and therefore use it more. Which leads to getting more karma.
Either of the two conjectures I advanced could explain a small number of users having a disproportionate amount of Karma.
High-karma users have followers. I've left comments on very old stories in out-of-the-way places and found them voted up. So we accumulate karma faster in part because people are simply more likely to see our posts, because they go out of their way to do so.
So, to an outside observer, you might suggest that these users game Hacker News but the real answer is that they have an audience. It's debatable whether that's their fault, on a case-by-case basis, though.
Then you could probably say it goes the other way: a large part of the community feels a certain way because Ed says so (in the top position), or Thomas says so. I've noticed the atmosphere of a thread change after a comment from a "well-known" person is left, rather rapidly on occasion. The momentum of a community like Hacker News is an interesting study, and although I didn't get an opportunity to watch the thread under the microscope, I bet a large part of it was shaped by Ed's comment.
Recently I've learned how Hacker News threads are living organisms, and I've noticed the impact of the commentary that I make. If you pay close attention, you'll be surprised at how the thread evolves and grows, particularly based upon what's in the top position.
