I finally got my super Keeneland database put together, which is a collection of every starter and result since the beginning of the Polytrack-era in the fall of 2006. I'm a little pressed for time today so I'll have to dive into the numbers more in the future, but I wanted to highlight a couple of quick stats with respect to two-turn graded stakes races on the eve of the 2011 Fall meet.
Since the Fall 2006 meeting, there have 46 Graded stakes races contested at a mile or longer on the Polytrack surface. Those 46 races have had 453 total starters. Of the total amount of starters, 92 are horses that have never started on a turf or synthetic surface, or roughly 20.3% of all starters. Of those 92, only three have won and the total record for "dirt only" horses in those races is 92-3-9-10.
Those three winners were Great Hunter (G1-Breeders' Futurity; 5.80/1), Little Belle (G1-Ashland; 16.10/1), and Grilla (UAE Cup; 3.70/1). That UAE Cup is an Arabian race, so the numbers are actually even a bit worse. (If you take out the Arabian race, it's 87-2-9-9 for dirt only horses).
Furthermore, 11 dirt-only horses have gone off as the favorite in those 46 graded stakes races, and none have ever won. The record for dirt-only horses that have gone off as the betting choice is 11-0-3-0.
While the Polytrack at Keeneland is fairer than you might think to dirt-only horses in many of the events (especially sprints), two-turn graded stakes races have seen those types of runners win less than their fair share. Dirt-only horses make up 20% of the starters in two-turn graded stakes races, but only 6.5% of the winners. Conversely, horses with a start over turf and/or synthetic represent 79.7% of all starters (361), but 93.5% of all winners (43).