But the truth is that innate differences matter not just in athletics, but in any endeavor. Even the famous Polgar sisters you mention both trailed men who had later starts and less formal early training for their entire careers. UK marathoner Paula Radcliffe's career is similar in many respects.
In general, the "purer" an endeavor is the more decisive innate differences are. By this I mean that innate differences will matter more for runners than for basketball players, more for speed skaters than hockey players, more for mathematicians than for hedge fund quants, etc...
But there is a great deal of evidence that innate differences create uncrossable chasms in skills far outside of athletics.
Music: http://news.bbc.co.uk/2/hi/health/1209186.stm
Motor Skills: http://news.bbc.co.uk/2/hi/health/1209186.stm
IQ & Cortical Thickening: http://www.nytimes.com/2006/03/30/science/30brain.html?_r=1
Language: http://www.sciencedaily.com/releases/2005/05/050517063228.ht...
Facial recognition: http://www.wired.com/wiredscience/2010/01/face-recognition/
None of this means that willpower doesn't matter. Of course it does. However, at least accepting the reality that we don't all have the exact same potential at every pursuit can be beneficial. For one thing, it's signal not to heavily invest in a tournament-style career, such as modelling or concert violin playing, unless you have a clear aptitude. Even for more forgiving careers, where merely being competent is enough to make a good living, it's rational to choose a career that aligns with your natural talents. Why put X amount of effort to be in the 70th percentile of some field when the same amount of effort would make you 90th percentile in another comparably in-demand field? Most people are happier doing what they're good at.