Actually, there are small physiological differances found in the skeletal and muscle fiber between the differant ethnic groups. As shown in earlier posts, it was found that generally blacks have a much higher percentage of the faster reacting muscle fibers which allows for much faster agility, thus the best sprinters are usually black. I could care a less if the guy is green with orange polka-dots, their physiology is slighlty differant. If it is not, then why do we all look differant? If there were no differances in our make-up, then we'd all be clones. We'd all look like alanbikehouston. (Sorry, I just had to).
As with any sport there is always the exception to the rule. The white guy who won the gold medal is of course one of the rare competitors who happen to have the ability to do so. But, out of the hundreds upon hundreds of gold medals awarded over the last 2 decades, very few, if any, were of white athletes for sprinting.