Amazon adds value compared to a physical bookstore because they have many times more titles, including many obscure books that aren't profitable to house in a retail bookstore (the long tail). Unless there are desirable, differentiated pet products that aren't profitable to stock in a store, then the internet model doesn't add value. Are there really a million different kinds of pet food that people could tell the difference between, let alone want to buy? That's the difference between Pets and Amazon.