isn't japan only using 100v outlets? i would think that a country with as advanced a public infrastructure as Japan would have adopted the most efficient socket standards to power their electronics.
I have no idea why Japan uses 100V for home wiring, but don't be too sure about Japan adopting the most efficient standards. Almost all the plugs and sockets you find here are ungrounded. Half the country is on 50Hz, and the other half uses 60Hz. I don't think these are deliberate choices. It's just that the opposition to change can sometimes be mind-boggling here - from a foreign perspective.
So even if the US moves away from 110, you can always bring it over to Japan, since I'm sure they'll be using 100 until the end of time.