Actually gringos was originally applied specifically to Americans.
Mr. Google will tell you: ".......There is a popular story that gringo meaning came from the Mexican-American War during 1846 to 1848. The story goes that the U.S. military wore green coats when they were marching through Mexican territory. In response, the Mexicans would say, “Green go home!” These words meshed together and the word gringo was born........"
We personally know quite a few Mexicans who DO differentiate between the two, so I'll have to stand on Mr. Landry's side on this one.