Someone with the exact same measurements generally has the benefit of being able to try the different sizes on, photographers often don't unless working with a company rep on hand, or they've sent multiple sizes which often only happens at the higher end.
However, I find the practice misleading in catalogs and in-store displays. The expectation in catalogs is to present the wares the seller is advertising. Using clips and pins misrepresents the product.
I really appreciate transparency and clarity in exactly how a garment is cut. Some sellers accomplish this wonderfully. One such seller is Mr. Porter. On their online catalog, you can see that some garments do not fit perfectly on the model because that is simply how the garment naturally hangs without clips/pin/tailoring. They also give the model's measurements so that you can compare your sizes to the models and a size chart. This has been enough for me to accurately judge how a garment will fit me even without trying it on! (Example: http://www.mrporter.com/product/301852 , select "Size & Fit"). Another website that does this is Amazon's myhabit.com
I don't mind GQ using clips and pins. GQ is presenting what is possible. A store, on the other hand, should show what they are trying to sell, and I believe using clips misrepresents their wares by obscuring the exact nature of their wares: sizing, cut, how it hangs, what would have to be tailored, etc.