The Wang Zhizhi thing was more serious than most Americans know; he had technically "defected" to the USA in attending Clippers training camp rather than returning to the national team. His passport was revoked, the whole nine yards. Unluckily for him, he also wasn't good enough to stick as anything beyond an 11th man on an NBA roster. Result: public apology to China, but to be fair he's now once again a national hero. The thing about Yao and thing about a lot of citizens of other countries in the world is the rampant nationalism involved in being a citizen. Being a US citizen isn't necessarily a big deal to an American; we accept for granted that the US is the most powerful country in the world and that we're better off than almost everyone. There's much less competitive drive UNTIL we find a rival--case in point, USSR during the Cold War or even the rest of the world in basketball now that we've surrendered our international primacy. China, however, is a rapidly developing country with a strong tradition of nationalism. Chinese too believe in their inherent superiority. The difference is that China is not the center of the world as it once had been. To represent one's country is the highest of honors, not some sacrifice to be given so that one has the opportunity to play ball abroad (in the NBA). Yao's stated himself, that his ultimate dream is an Olympic medal for China rather than an NBA championship.
