Intersting thread! I actually have alot of int'l experience due to my love of travel and foreign languages.
I spent the Summer of 2002 studying Mandarin in Taipei, Taiwan. I rented a room from a middle-aged Taiwanese woman that loved to practice speaking English with me. She told me that all she knew of Americans she gleaned from TV...therefore to her American = white (not me), blonde haired (me), blue eyes (me). But when I tried to tell her that I was black, I swear she thought I was pulling her leg. To this day, I'm certain she didn't believe me.
I didn't take offense because I realize that her ignorance resulted from a lack of exposure.
I'm not surprised that people have such a homogeneous view of Americans given that w/b/b is an ideal that is heavily promoted in the media. Also, it reflects the general lack of knowledge that people tend to have about things outside of their own realm of experience.