Not really since it does not take a substantial investment and/or a large concession to convenience to be able to go to another supermarket to buy a given good. Once a person has paid Apple for one of its products said person would have to either commit to buying and carrying an additional non-Apple device - another investment as well as a compromise in convenience - or forego on the Apple device altogether by replacing it with a non-Apple type. If Walmart behaves in an annoying fashion you can just walk to the next store.