The Chinese and Japanese are two obvious groups, at the very least.
I recently spent three months traveling through East Asia, mostly in China (Beijing & southwards) and Japan (Tokyo & southwards). There is a huge amount of casual gaming compared to Europe and the US. People commute a lot using advanced public transit (even Beijing's subway looks like Sci-fi compared to NYC MTA, and of course Japan is a different planet altogether). So, all these people not busy steering (and gearing, if in Europe), have PSPs at hand for zoning out to and fro work. And it's not just young boys; also thirty-something women frequently whip out gaming gear rather than makeup kits.
Of course it's not only a subway phenomenon. In Japan for instance, apart from all the gaming at home, there are also at least three distinct types of public game venues:
1 - Tekken-style penny arcades, similar to those in the West, mostly crowded by young men.
2 - Incredibly packed places with Vegas-style machines, but with small silver balls that rush though mazes. These places are unbelievably noisy from all the balls, sounds like a small airport. People of all sorts hang out here, from young men in fancy suits to middle-aged women who apparently just drop in when shopping.
3 - Cafe-style manga libraries where there are also booths for reading, gaming and surfing - or just sleeping. The Japanese seem to be sleeping everywhere, even in the lobbies in the hotels where they stay for the night. I really don't know why they prefer the lobby to their own room..?