In an effort to try to win the most golds at the Olympics, they spend extra recruitment efforts on sports that have a large number of medals awarded (like swimming). I'd be curious as to how much doping they have going on now; the 1990s Chinese women's swimming team was particularly blatant: only good in sprint events, deep voices, acne, and hugely discontinuous drops in time (and a men's team that wasn't even on the radar). Actually failing drug tests a ton of times surely adds some support to the view of widespread, East German-style doping at the time.
There was even an interesting bit about Chinese ping pong dominance (and how it came to be):
Consider the country's decades-long dominance of table tennis. This supremacy had little to do with a national passion for wooden paddles and plastic balls. China decided to develop star paddlers largely because the International Table Tennis Federation was, in 1953, one of the first sports organizations to drop ties with Taiwan in favor of the mainland. In 1959, Rong Guotuan made history as China's first world champion in any sport. Mao deemed the victory a "spiritual nuclear weapon." Determined to maintain Ping-Pong supremacy, coaches fanned out across the countryside looking for kindergartners with quick reflexes and superior hand-eye coordination. "Other countries have produced some really good table-tennis players," says Liu Fengyan, director of China's table-tennis administrative center. "But without a sports system like China's, their success ends when those athletes retire."