I'm not sure if we were all watching the same women last night, but the Americans do have breasts, and they are fantastically muscular. They eat right, and do not starve themselves. Little Girls in Pretty Boxes as written in an era in which gymnastics belonged to children, and a girl who developed curves generally was not able to continue an elite career, which led to a rise in eating disorders in the sport. The book is not the most balanced look, either. This has changed pretty significantly over the last decade, which is why you see Mo and Annia in their twenties on the US team. This is not to say that some girls in gymnastics become overly body conscious, but don't paint with such a wide brush.
This is a fantastic sport that gives girls like mine, who put up with being called shorty at school and mistaken for a 5 year old by adults. (She's turning 9 in two weeks.) She's finally found something that fits her stature. She's blossomed into a confident, sparkling, coordinated young lady thanks to this sport.