This has to be a record -- I posted on this thread six weeks ago!
Anyway, the dollars never have to come back to the USA. The dollar is a global currency. Dollars have been deposited overseas since WWII. Foreign transactions are settled in dollars all over the world.
The strong nations since the War (Germany, Japan) built their reserves in dollars, not gold. Same now with India and China and South Korea. The Dollar is as much a part of American Global Power and influence as our military and our global brands.
Why is the Dollar so strong? Bewcause it's the currency of our free country -- free politically, free financially. Taxing transactions in this country would be an unmitigated disaster, and nobody with any knowledge of our economy or international finance would seriesly consider it.
Umm they do if you want to spend them here. Food, Clothing Housing, Bills, etc...