Macy's gives a refund if the price on your purchase goes down within X days. X is not overly generous, but ... it's better than nothing! You don't have to bring the merchandise back, just the receipt. (Hence, it's smart to go shopping a couple of days before those big "One Day Sales!")
Circuit City used to give you the difference plus 10%. I'm not sure if they still do, but I remember receiving it on a TV once. I just happened to be in the store looking for something else, and saw "my new TV" for a significantly lower price. I didn't even have my receipt with me -- they looked me up by telephone number and immediately issued the refund ... well over $100 if I remember correctly.
It's good business -- makes the customer happy. And happy customers are repeat customers!