I'm not familiar with this stereotype but I haven't spent much time outside of the US. Perhaps part of it is that fact that so many minorities in America insist on segmenting their background. Someone brought it up and it's a good point, there are now Asian Americans, African Americans, Mexican Americans, etc. etc. Well the majority of my ancestors came from Europe but I have never been to Europe so why call myself "European American"? My cultural background is much closer to the Mexican heritage but I was born and raised in America so why be a "Mexican American"?
"White" people couldn't even get away with catergorizing themselves if we wanted to. Anytime a group of white people try to unite for whatever reason they are required to open their ranks to anyone or be called the KKK. Well, I couldn't join my high school's Black Student Union or Asian Club, if our labels are so strongly associated with our bloodlines (thus the line "The only real American is a Native American") why can't "my people" study their background.
Because of this problem, white people are simply American. Everyone else is xxxxxx-American.