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.