China pegs their yuan value to the dollar (8.3 to 1), guaranteeing their products will be quite a bit cheaper.
Japan doesn't, the yen floats.
I probably shouldn't have put the exact ratio on costs in since it may not be that, but there certainly is a good deal of disparity in costs. It would be nice of the difference was less than 8 to 1.
Here's the best article I could find on this:
http://www.bradenton.com/mld/bradenton/news/world/6556460.htm Four U.S. senators last month sent Treasury Secretary John Snow a letter urging him to "investigate" China's currency strategy and take steps to protect American business. The two Democrats and two Republicans agreed that the yuan is undervalued by anywhere from 15 percent to 40 percent and gives Chinese exports "a nearly insurmountable advantage against United States producers," the letter said.