Alright, so it does look like the results are skewed. They are using the metric of the world ranking of the player who gets drawn as seed 1 or 2 first round opponent. I think it became this way due to the fact that USO has had draws of significantly lower ranked players than only the 33-128 that the simulations include. Naturally, when you have an outlier like the 518-ranked player () the average is now going to be heavily skewed downward. To the degree that the running average simply cannot be reflected properly by a simulation that only goes to 128. This is my guess. I think it would be borne out if we can look at the average world rank of the unseeded players in the draw for each tournament. If this is the case, I'd expect that we would find that the average rank of players in the draw for the USO would be lower than the rest, followed by Wimbledon, then French and Australian would have comparively higher average unseeded player ranks. Or, the way to correct for this bias would be to assign a player a rank associated with how their current ranking matches with all of the other players in the draw, thereby assigning the lowest player a rank of 128, and try running this again. The average world ranking metric is inheriently flawed for this analysis.