Supply VS Demand.
Regardless of the exchange rate, Japan consumers are willing to pay a higher price and get better service. You won't find many discount retailers in Japan. Online shopping and credit cards are not as popular in Japan as in the US, and you will most likely pay a premium price in almost any major city. I wouldn't trust anything sold in China.
When I visit family in Japan, I load up with Japanese and American electronics to bring with me. When I was in Japan last year, I brought a new Dell Laptop ($548 online from Dell Outlet vs $1,700 in the Japanese electronic stores), and two new iPod Nano's. (A model not even available in Japan at the time.)
To avoid issues with customs, I just didn't take the laptop box... I placed it in my carry-on.
Other items I bring from the US to Japan to save money include TV Splitters, HDMI Cables, Wireless Routers, Network Cables. I also have brought a Slingbox which I packed in my luggage.
Levis Jeans, Sneakers, Gloves, Underwear, Toothpaste, Deodorant, EYE DROPS, TYLENOL... Bring as much as you can or you'll pay 4x's more there. You won't even find Tylenol, Advil, Ibuprofen. If your shoe size is larger than US size 9 forget about buying anything in Japan. Get a haircut before you leave, unless you want to spend $40.
Another thing... memory cards. Bring them or you'll pay!