Re: "I had expected that people would read posts and comments by other people, and take special note of comments by people who had a prior history of being right, and thereby improve their own accuracy."

FWIW, I think that was how I originally approached the problem. Rather than trying to solve it directly, I first looked at your response, and Robin Hanson's response. After a little reflection, I concluded that you agreed with each other - and that you had both focused on the key issues - and got the answer right.

At that time, most of the rest of the thread was people saying the problem was ambiguous and needed a bet to clear it up - and a fair bit of confusion - with very little defense of the standard answer.