According to analyst Michael Pachter, the weak dollar is behind the reason for the Wii shortages in the US.

With a weak dollar, foreign companies that sell their goods in the U.S. for dollars and then convert those dollars to their native currencies get a smaller profit than if they sell their products in countries with strong currencies of their own (such as Europe with the euro). In other words, Nintendo makes a bigger profit on Wiis sold in Europe than on Wiis sold in the U.S.

So Nintendo, Mr. Pachter said, has been behaving perfectly rationally by sending excess Wii consoles to Europe to satisfy the more profitable consumers there.