I first saw it discussed in either Malcolm Gladwell's "Outliers" or Dubner and Levitt's "Freakonomics". They sort of blend together in my head because I read them both over the span of a couple days and they touched on really similar themes (which I hadn't expected), but I suspect it was the former.

Wherever I read it, they listed it as just one of several reasons Asians tend to be good at math, with cultural factors being another important factor. Something about how, while Westerners generally had to just plant wheat and similar crops at a specific times and they would grow fine with a base amount of effort, the yield of a rice paddy was directly related to the effort put into maintaining it. According to them, this ingrained (hah, grain) into Asian societies the idea that your success is directly proportional to the effort you put into something.

I haven't studied it myself, but I thought that theory was interesting.