This is a really interesting debate, I'm a student in the fashion industry just now and it's bugs me greatly the size we have to make our collections to. We are told it's a standard British size 12 but when we took the measurements it's about the same as a store size 6.
It's true clothes do look much better on a slim tall person but I think there's a line where they become too thin, this is a video I love of Cameron Russell doing a Ted talk.
http://www.ted.com/talks/cameron_rus...m_a_model.html she talks about the insecurities models feel etc.
Also I'd like to note that there are people in the fashion industry trying to make a change, but a select few can't do it alone.