This sort of extreme economic consolidation hiding behind an apparently wide range of retailers and/or brands is very common. You could make the same observation, say, of laptops (Foxconn), consumer goods (Proctor & Gamble), or ag products (Monsanto, ConAgra).
Most of the sunglass brands that people know, and the stores they buy them from, are owned by a single company:
http://online.wsj.com/article/SB1000142405274870451890457536...