Same concept that airlines have been using for years now - the less elastic the options, the more the company can charge. Tactics like this are just simply banking on the the fact that below a certain threshold, it's just not worth the time and gas to shop around.
In fact, I believe that this is why Baskin Robbins has a rule against opening up a franchise too close to an existing competitor.
The online marketplace is nearing perfect price discrimination. Staples is not lying to or deceiving anyone; they're charging what they expect people to pay in a given area. If someone doesn't want to pay a local non-competition premium they can easily go to another website. Nobody is forcing their hand.
And you can beat the system. I routinely order from a national chain. I have to select a location. I pick a major metro area ( normally Norfolk Va). I place my order and tell them I want to pick in up in the store. I choose my location. I can save anywhere from 10 - 25% each time.
Turns out most people have been successfully conditioned on how to think. Everyone is arguing on behalf of businesses, whose near sole purpose is to externalise as many costs to the customer, as well as charge as much as can be gotten away with. Yes you can choose to shop elsewhere, it doesn't make it ethical though; just as the fact that socio-economic based pricing being the norm does not..
Prices also act as signals. By raising prices in the zip codes where little supply exists, it will create the signal that might allow more supply to that zip code to be created. Also, Amazon allows 3rd party sellers, who cannot use such software as they cannot know who the customer is before purchase - they would compete against the price difference being too high. There are also price comparison apps, like Invisible Hand. But good job stirring up the fairness brigade - on Yahoo News they are already talking about new laws that need to be passed.