Paolo Bacigalupi says it much better than I. His experience is as an American in China, but it works for Japan, too.

I experienced the very same thing about supermarkets after coming home from nicaragua. I remembered the empty aisles of a large market in Managua, and then cried seeing all the kinds of peanut butter in my hometown's grocery store.

Here is the quote from an interview in The Mumpsimus (a review blog for genre fiction that is intelligent and interesting)

"If you spend enough time away from your own country, it sort of poisons your psyche. You never get to be a pure American again, because there's this foreign part of your brain that's been jammed in as well. It gives you a bit of double vision when you look at things. And I think that sort of experience, looking askew at the world, also helps me write, somewhat: that off-kilter sense that everyone else thinks something is normal, but you can't quite get on board. The classic example that I hear a lot from people who've been in the Peace Corps or spent a lot of time in a poorer country, is their first view of a supermarket when they return, with its aisles and aisles of food. It seemed so normal before, and yet suddenly it seems perverse. "

http://mumpsimus.blogspot.com/2004/09/conversation-with-paolo-bacigalupi.html

And that's why Naoto can never be Japanese again and why I am only partially an American.