I always hype up Slate.com on here, and it is articles like this by Huan Hsu that keep me coming back. I find his analysis of the problems of USA Tennis right on, and it ties in with others theories like the 10,000 hours principle extolled by Malcolm Gladwell in Outliers (highly recommended by me) and the dip of Seth Godin. If you just follow the established training regimens for tennis, you probably won't be a Grand Slam tournament winner, even though you'll surely be psychologically broken if you do have a nutty parent. (Example: The father of Jelena Dokic [left] claimed that her boyfriend had kidnapped her, and was so abusive he was banned from courtside at pretty much every tournament.)
It is kind of a logical supposition to make, although one that isn't always apparent. Professional athletes largely come from broken or nutty homes. How else do you practice basketball eight hours a day unless the parents are a bit absentee and you let your homework effort slide? Natural ability and aptitude do come into play, but they are only part of the equation. Insane devotion spurred by parents helps.
I imagine this is an even greater issue in individual sports like tennis, boxing and swimming. At any given time, I'll guess that only 100 to 500 adult boxers, tennis players and swimmers are good enough in the world to make their primary living from the sport. Since all of them are individual sports, there is far less opportunity to earn a living. Contrast this with baseball - Even AA and AAA players often make as much as they would in jobs they could use their degrees (assuming they have one) on, and there are hundreds of teams, plus thriving Asian and Latino leagues, all of which need roughly 20 to 30-man rosters. A rough estimate of that gets me to 3,000 players. More players means a greater opportunity for different personalities.