Uhmm the US has a huge huge huge military presence in South Korea. Many of those XBOX 360s are probably brought there.
It's not quite that big. Maybe about 37k total currently. Maybe less. They've been scaling back military staff there in the wake of Iraq. Simply not enough troops to spread around globally. Prior to 2003, Korea was a non-deployable duty station; not any more.
Finding video game gear through the PX system is not always a given. Partly due to black market purchasing. It's cheaper to buy through the PX (everything is tax free) if you find someone with PX privileges (not Korean nationals; even those who work on post) who is unscrupulous enough to move goods to Korean nationals, which is illegal unless it's given as a gift. But of course it happens anyway, even with the sales tracking system. Liquor in particular through the PX system is a hot item because of the difference in prices relative to the local economy.
So the number of consoles being shipped to major installations like Camp Humphries, or Yongsan, Seoul is not actually a huge amount. PX shelves often go bare of consoles, even back in the States on military installations, much less overseas.