These values are far more arbitrary then I like to admit.
NOW you are speaking some reality.
Well, I hope you understand what is "reality"? You are too afraid to speak about what reality is.
In the 1990's, certain Asian countries like Thailand, Singapore and South Korea didn't have any gold to use as their standard to back up their currencies. So, they used the US Dollar. Now, since the US Dollar wasn't their national currency I believe this was a big mistake for them.
Well, in 1997, an economic event called "contagion" spread through these "Tiger Economies" as they were called and ate up all their dollars and completely devalued their currencies, even in their own countries! Devastating to their economies.
Of course, the International Monetary Fund, IMF, came from the United States and forced certain political changes for bail out money.
Well, in a cash based economy we would use our dollar to back up all our debt! We can do that since it is our currency. Consequently, there isn't any fear of a crash since there is a dollar for dollar coverage for all our debt. What would happen with foreign currencies couldn't harm that set-up.