A site called RetailSails has done an analysis of the top global moneymaking retailers per square feet of store space, and guess who comes out on top? That's right, it's Apple, who reportedly picks up over $5600 a year per every square foot of retail store space. There is some confusion and estimation here -- Apple is opening and closing stores all the time, and the company only releases sales numbers for retail on a worldwide level, not just the United States. RetailSails has done its best to get the numbers right, but even they admit this is designed to give more of a general insight on the scene rather than specific figures.
All that said, there's no question at all that Apple is doing an amazing job with its retail divisions, designing impressive stores in all the right places and making sure that those stores deliver on sales and revenue expectations. Even a store like Tiffany and Co., which tends to be smaller but sell relatively more expensive items in general, can't keep up with the revenue Apple has flowing in.
It's no wonder, then, that Apple keeps posting record sales, and opening new stores as fast as it can. If there's a ceiling to demand for these products in these spaces, Apple hasn't hit it yet.