I'm skeptical that Walmart can really beat Amazon via logistics. They're both top-notch operators in that realm, but Amazon's product pipeline is a huge advantage - they don't have to manage nearly as many locations, nor do they have to hold as much inventory relative to sales volumes because they have fewer fulfillment centers.
And their Subscribe and Save program (which offers a 15% discount on common household products) is aimed directly at Walmart and the price clubs. (http://www.amazon.com/gp/subscribe-and-save/details/index.ht...)