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".
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).
Numerous historians, including coffee history specialists stick with the WWII origin. Indeed, http://atwar.blogs.nytimes.com/2013/08/16/the-marines-secret... *provides a picture of a Marine drinking an "Americano" style coffee in 1944 and documents the role of coffee in the US Military back to at least the civil war. See also http://www.vanhoutte.com/en-ca/c-the-coffee-blog/coffee-cult....