When he has a company registered in a country(USA), than yes it is the duty of another country(Japan) to extradite him to this country(USA).
You are right, that it doesn't depend on where the customers are from.
Thanks for making it clear. I was getting a little bit confused.
Watch: this makes the news. "US pressures Japan to turn over Bitcoin criminal who lost victims over $600M."
I don't care much about the news headlines. The Mt Gox scandal has already did huge damage to Bitcoin in terms of publicity. It will not get any worse now. The important part is that Mark Kerpeles should be brought to justice.