I partly agree with this. USD is the name of American dollar, so it is better to link it with U.S. However, don't forget that the currency cannot be limited to anything, especially if it is electronic USD (USDe). It should be an international currency everybody can use, it is the electronic dollar that everybody can purchase anything over the internet. So it can be centred in US, but can be used by anybody with no conversion needed if the payment method accepted by the merchants over the internet.