Instead of asking why people abroad keep taking our excess dollars, I think it would be better to ask why they should stop. You can buy anything you need to buy, price anything on a world standard and save your money at any level of risk/return in the most liquid capital markets. So long as the US keeps making bond payments and foreign exchange reserves are, in the main, held in dollars to protect *other* currencies, why not save in dollars?
Meanwhile, the third world is in a perpetual currency crisis and economies driven by exports to the US struggle to keep their currencies from rising too quickly and killing their price advantage. So it seems to me you have non-dollar assets perpetually deflating while people glady accept excess dollars because they know they can use them and they know what those dollars are worth.
boddi