In fact, Apple stores have the highest per-square-foot revenue in all of retail. The only other retailer that comes close is Murphy USA, which is a chain of tiny gas-station convenience stores that are crammed with high-priced snack items, tobacco, beer and wine.
I doubt they even get close. Apple's $ per square foot per store average Revenue is over $8000. Tiffany Jewelers on 5th Avenue is second at a bit over $4000 per square foot.