From what I've heard, the designers choose tall models (not too tall though; I think 6' + models are harder to cast, and I hear that their agents will usually lie on their cards and say they're something like 5'10" 1/2 or 5'11") because the clothes hang off them like hangers. We, as consumers, are supposedly supposed to find the look attractive.
As for my height, I'm 5'6", and when I was looking at the average heights around the world, all my countries are European (Austria, Belgium, Czech Republic, Holland, and Norway). I'm tall according to US standards.