I think you guys are missing my point a little bit. Why do people go to stores in the first place when they can buy just about anything they want on the internet these days and have it delivered to them, often for cheaper? Why do they go to the movies when they can simply watch television, and order whatever movie they want? Why do they go to public restaurants, when it is much cheaper to purchase the food you want at a market and prepare it yourself, or order it made and delivered?
The answer to all these questions, according to sociologists, is the same: because people enjoy human interaction. Most people like being in a crowd of other people (despite constant assertions that they don't.) So as I wrote, you can have a few robots at your store helping people out, for convenience and novelty, but if you're imagining a large department store filled with robots with almost no humans helping the public, forget it. That's never going to happen, no matter how much money it might eventually save.