Currency is slightly more fungible than this. Not enough to invalidate your point, but worth noting that I've purchased food, transportation, lodging, and knick

Currency is slightly more fungible than this. Not enough to invalidate your point, but worth noting that I've purchased food, transportation, lodging, and knickknacks in Saudi/Bahrain/UAE and Oman using USD. All of the above items, in each country. It's certainly not a universal currency though, I'd say the vast majority of vendors were not interested in taking USD. Even then though, generally you could find a private citizen/local expats from many other continents that would be willing to perform currency exchange to/from popular currencies at a rate profitable for them. Vendors/citizens of some other countries - Jamaica, many parts of Mexico, many parts of Canada, also are happy to deal in USD as a customary business practice, at least in my experience.