Also, what's cheaper than using a currency which you have control over (read: ability to inflate; if one is in the camp that the conglomerate of national/international banks that own shares in the Federal Reserve act in unitarity with the USG) compared to most other countries, to import natural resources? One could call it free (if one doesn't factor the human beings on the other side of the equation...) Sure it can't last forever... but individuals don't last forever either.