Apparently the average cup size in China is increasing. It used to be that most bras sold in China were cup size A or B - but now manufacturers are making more of the bigger cup sizes.
On Inkycircus, where I found this, they think that the "explanation" provided by the Shanghai Daily - that Chinese women are becoming bigger-breasted due to increases in nutritious eating and participation in physical activity - is a load of hooey. They propose that increases in McDonald's consumption might be the real culprit. Some of the commentary from the peanut gallery suggests that it might actually be related to more hormonal birth control intake.
To me, either of the latter two explanations sounds plausible... but either way, I bet the Chinese MEN aren't complaining... ha!