NO! There are a LOT of big boob women in Japan. South Korea seems a bit lacking in the boob department though.
I remember a female American comedian or I guess it is comedienne. Thirty or so years ago, blond very thin and pretty. She made fun of herself for being flat chested, and to go along with that, she said " can I get a shout out to my sisters in Japan ? " After that I thought it was a given that Japanese women were well known for being small chested.