that is because the USD is the currency for he dging . the word economy or the Euro-area economy are recovering from the FINANCIAL crisis,and most countries of the world use the USD to hedge the FX risks; at the same time ,the word (except USA) kept the relatieve stable or lower exchange rate against USD in order to sitmulate the ex-port .so we can obviously find that the USD increases its value ,even the USA has a so big deficit .