If you read the first part (http://alg.livejournal.com/84032.html#cutid1), you read that all "accounts"--meaning B&N, Borders, Walden, Sam's Club, supermarkets, drug stores, etc.--all receive a discount off the cover price. This is so they make money when they sell the book to consumers. Their discount can range from 30% to 60%--or sometimes even more.

Go back and read the first part again (http://alg.livejournal.com/84032.html#cutid1); there's a lot more info there.