I will probably get flamed for my lack of knowledge on economics, but here goes...
I believe there is a reason that the exchange rate is talked about so much.
When the currency was originally issued, the goal was for it to be a 1=1 exchange rate with the dollar.
Initially, the rate was about $.80=1Euro. There has been about a 40% change in the ratio in the last 6 years.
The yen has never been valued equally to the dollar, so the comparison is apples to oranges.