Apple’s iOS and Mac app stores revolutionized software distribution. They provide one-stop shops for apps from vendors around the world, allowing software developers to offer their products without worrying about setting up distribution contracts. They also take care of the fulfillment (billing and downloads), saving developers time and hassle. In exchange, Apple takes a 30 percent cut of sales, which is fair for the service they provide.
But there’s one thing you can’t do in Apple’s app stores: you cannot provide a new version of your apps to existing customers at a discount. You can’t offer upgrade pricing.
Read the rest of the article on Macworld.