So why the big difference between Asia and the USA/Europe?
Well, (without being a racist) I suppose that:
1) Asian people are more fascinated by 'latest hi-tech things' and change/buy them more frequently than European and American consumers who prefer 'reliable long-time investments'.
If you're implying that Asians don't favour reliable long time investments, then I think you're wrong - at least at the more senior level of the population. The younger generation(s) are very much into what's new and hip (or at least that's what I see) but it might be a product of age rather than a generation.
2) Asian people like to travel abroad and use 'package' vacation type with a lot of organized excursions (e.g. a big bus full of tourists from Japan is a usual thing anywhere in the world), so they like light travel cameras.
Europeans travel a lot and they get proper holiday/vacation periods, unlike Americans who frequently only get two weeks a year.
3) Americans and Europeans, on the other side, either prefer to work in their sweatshop offices all year round (without going to other countries until they are 65 and too old to work) making only pictures of their barbecues, dogs and kids, or travel by car to places nearby, or have sea & beach family type vacations -- in all these cases camera size and weight do not matter that much.
That most Americans stay inside their country to travel and do so by car is, I believe, a big and important factor in what they buy. I've been at Yellowstone and watched a guy stop, open up the back of his truck and pull out a 600mm lens to mount on his 1D. You just don't pack that sort of gear when you need to fly.