I think it all comes to style and they type of clothes that a model wears that require whether what size model to choose, and this will enhace the image. Too be honest, I do like images of smaller models, not over someone that may be of a different size but due to the industry, the styling and art direction of these photos have been built on over the years with this look and this is how experts in the field are used to working. Take a bigger girl and a lot of people do not know what to do with them, and that needs to change. Less money is spent on shoots when using bigger models, there are of course so many less designers willing to make samples of their designs to advertise before the launch of seasons and therefore stylists have less to work with. These things are the things that need to change before we can honestly see more models of different sizes make it in both high fashion and commerical markets. In real life however my opinion is that a model never looks as good in these outfits when among regular people like you and me. They look thin and strangely tall and the glamour seems to be lost. I have met a few models in their down time when working in a london hair Salon and it really does become noticeable. Take a beautiful girl with Crystal's height and size, put her in a nice dress from Topshop and send her to a party and I am sure she would be the most attactive person there, old siren kind of beauty.
I don't really have a final concluding thought on this but it really does make you think and consider what the issues in Fashion really are and that it really isn't all black and white, thin and fat and tall and short. Let me know your opinions!