I think this is another example of the very common pattern of 90% of the contributions in online discourse come from 10% of the population with 90% of post coming from a 1% minority of the overall population. It's not unusual at all.
I have experienced no such limitation and never see it myself. Googling shows me the current policy is rate limiting accounts when they "post too many low-quality comments and/or get involved in flamewars."
I've been thinking about this after having read https://www.nngroup.com/articles/participation-inequality/ again recently. That research was shared in 2006/9. They didn't quantify a upvote/reward driven website but I suspect hacker news is closer to the blog numbers than the general, so the percentage would be skewed. The closest statistics would be Reddit's, the self selecting "top 1%" subreddit has imposed a minimum of roughly 107000 combined karma/points which is roughly 114k users out of an estimated 52 million daily, 430 million monthly, and 1.5 billion registered total users.
