I've never though about it, but what Americans call "regular coffee" in my country is called "American coffee". When I ask for a "coffee" I probably get a latte or in Spanish "café con leche".
Not quite. The "Americano" (espresso with hot water) common in countries with the espresso coffee culture was invented during WW2 when the GIs requested bigger cups of weaker coffee.
The american "regular coffee" is (weak) drip brewed coffee.
1. That origin is just urban legend. Americanos started in the 70's.
2. Per ounce, you're technically correct about the strength of espresso vs. drip/brewed coffee. But brews have variable strengths, and most Americans drink 12, 18, and 24 ounce drip coffees (which ends up being more caffeine than even a quad shot of espresso).
Regarding #1, the urban legend legend is itself an urban legend. The only sources for "Americanos" originating in the 1970s is a dictionary entry and Wikipedia, neither of which are further sourced or authoritative.
2: I mean "strength" in a broader sense than caffeine content. I get more jittery from drip coffee (or french press, my personal poison of choice) than I do from espresso - I seem to recall having read that a shot of espresso contains less caffeine than a cup of regular coffee because of the quick extraction. But espresso has a much more intense (stronger) flavour.
