Some people design their music specifically to be listened to with no distraction. Some people design their music to be listened to repeatedly for hours on end while (more often than not) focusing on other things - ie, a video game plot/fight/whatever. It's also worth noting that you get a lot of rock in the middle of gaming music, while you don't get so much of that in a symphony orchestra (obviously - not many people would go to a symphony orchestra to see a rock concert!). So again, it's two different fields that are, well... different. I imagine that Japan has composers who don't deal with gaming and, for all I know, they get more classical album sales than the gaming industry does.