The engineer in me wants to figure out if one could codify hips, bust, waist, and leg length to get a 4! set of combinations but I can't imagine any store that would buy 24 alternates in small, medium, large, and XL, that is 96 copies of the item just to sell one to someone. Not really economical. The thing that really bothers them though is when a supplier has reliably supplied the same size for several years and suddenly changes manufacturers or something and wham it doesn't fit.
It certainly suggests that roboticly made to order clothes would be a winner (Google could try that with their robotics companies) and one of the big obstructions, the sewing machine, is slowly succumbing to automation
[1] http://motherboard.vice.com/read/automated-mini-factories-wi... [1]