People are sort of missing the big picture on this one. While Potter fans are steaming into Asda to buy the book at a £1 a go, they are in the store! How often do you go into a store and only buy what you went in for?
The influx of people who might not usually shop there will more than make up for their loses as people will buy other stuff. Its all about bringing in people as new customers. Which they have done really well as now people who don't shop at Asda are now heading down there just to get the book. Where I am sure there are lots of flashy banners for all sorts of other wonderful deals to lure people in by