The thin look was made fashionable by the supermodel Twiggy in the 1970s. She really made a huge impact on the culture. Before Twiggy, women were thicker and it was common to wear a girdle. Look at any playboy from the 50s and 60s to see the difference. I agree that the supermodels are chosen to look like boys. The pictures are self explanatory.
http://en.wikipedia.org/wiki/Twiggy
http://en.wikipedia.org/wiki/Twiggy
Rico... Sauve....