Just curious, where did you read that article? I'm a fashion design student and there's really not a "norm". It varies depending on style, the model's agency, region, designers' preference, etc. For example, models for Christian Dior and Prada are generally very slim like you use as an example. However, models for houses like dsquared2 and Dolce & Gabbana are usually much more muscular. Also, there really isn't an organization that tracks all of this data because there are so many different model agencies worldwide. Not trying to start any arguments or say that there isn't often a problem, but I would simply question the reliability and the source of that information. Oh and this is my first post here, so I'm hoping I didn't step on any toes, just putting in my two cents!
-Will