The U.S. dollar's effective exchange rate since 2002 steadily weakened up to 2012, before rebounding somewhat. However, it didn't weaken as much against ALL currencies as it did against the currencies of the major developed countries (which include the pound and the euro). This could be because:*

1- the large trading partners, China and Japan, did not allow their currencies to appreciate greatly against the U.S. dollar.

2- the rate of appreciation is always somewhat greater than the rate of depreciation.

3- the United States does not trade with some nations, so the effective rate is biased.

4- the U.S. government has a strong dollar policy.