Dollars are the international reserve currency, like it or not (and believe me, Russia and China don't and are trying to change it). But for now, that means dollars are the most convenient form for buyers and sellers, typically.

Also, if the currency is of lower value, they get paid more. Example being the English pound is of a higher denomination than a dollar, but whether it's "worth more" is dictated by purchasing power, relative movement over time, etc.