Yes, but anyone who has information about their immediate percentile-neighbors (but nobody else) now 2 data points (their own income-part of society and the sup

Yes, but anyone who has information about their immediate percentile-neighbors (but nobody else) now 2 data points (their own income-part of society and the supplied data point) and so unless they're around the 50th percentile themselves you have supplied them with a ton of information. I think it would have been far more instructive not to include that data point: people's guesses also would have been more revealing (the last, aggregate-guesses graph on the results page). (Especially since we can have a good idea about who the guessers are - readers of the NY Times who choose to complete this specific graph exercise.)