The photos on this were taken at a Uniqlo store in San Francisco.
I go to Japan every year so I saw the first Uniqlo store there, not too many years ago. I bought several long sleeve shirts because they were low priced and high quality.
Uniqlo has grown to be a global retailing giant. It is now forth in gross revenue after H & M (Swedish), Zara (Spanish), and Gap (San Francisco). Uniqlo is growing the fastest.
This is the most comprehensive article on the marketing methods of the four stores. Zara is the most automated and can catch trends the fastest. Uniqlo is the most analytic and goes for a trend in a core style.
Last year Uniqlo opened a new 8 story store in Ginza. On each floor above the first were a row of rotating mannequins behind a glass wall. Inside the store were similar mannequins arranged to show the goods on each floor. The heavy use of mannequins seems to be a Uniqlo innovation.
On this page I have photos of the use of mannequins in Uniqlo stores, even on the upper walls. The most surprising is the use of miniature mannequins on the outside of the store, a tiny version of the Ginza store.
To me, the use of mannequins to show the near infinite variety of combinations of clothes that are stylish and possible, appeals to the current fashion trend to: 'be unique but still well put together'. It is a way to stimulate fashion imagination and make a limited store inventory look very large.