i think the physical potential is there, the main problem lies with the way most asians' minds work. ill speak from the japanese point of view. from a very young age, children are raised to be successful, honor their family, be humble, and not live with shame. because of this, the majority of the kids focus on excelling in school work and try to earn a high status the "normal way". in america, kids are taught to dream. for instance a youngster who is a very talented guitarist might say he wants to start a band and get famous, not go the usual college route but instead pursue his dream of being signed. another child may focus on his athletic skills, and spend all his hours after school training because his dream is to become a professional athlete. these things more than likely are looked up on by the american society because it is one born of dreamers that wanted something more. however, in japan these things would be viewed as 'unrealistic' or too risky to end in complete failure (being a bum on the side of a street).
there are the ones that are born as athletic freaks, and their parents push them to be their best at their talent. once one of these children find their talent they will train and push and strive to be their best resulting in athletes like ichiro, suetsugu, shunsuke nakamura. however, there isnt as much open-participation in organized sports like there is in america. for instance, almost no college in japan has athletics. they focus purely on academics. in this way after high school, many children need to choose, am i good enough to turn pro now? or should i quit my sporting ambitions and go into the workforce? there really is no in-between process of letting your body develop more.
the athletic ability is there. physical education is taken very seriously. children must pass certain tests in PE just as they would in math or history. for example, leapfrogging a certain amount of stacked gymnastic blocks to pass the first grade, being able to do 10 chin ups, and swim 50 meters free-style to pass second grade, and so on. (some exceptions are made)
the national media is there. whenever japan won that first world baseball championship thing a few years ago (anyone remember?) the country went crazy. when the soccer team advanced into the knockout stages in the 2002 world cup, or when suetsugu medaled, it was a huge huge deal. the main problem is that most children are suppressed by this idea built into them from feudal age society that doesn't allow them to dream. they instead try to be the very best at things they can 'control'. if more would develop the mindset like the ones i previously mentioned i know that japan, for one, would produce more world-class athletes in all sporting events.
sorry for the long ramble, but i thought i would throw in my insight as i have personal ties and experiences that i dont think others here would have.