For an interesting take on how two massively successful corporations operate, just take a look at Microsoft and Amazon. Both companies offer apps that rely upon users buying a subscription. When Microsoft released their Office suite for the iPad, they made it free, but users needed to buy an Office 365 subscription to access premium features. Amazon just bought the comic book reading app Comixology which also lets users buy and subscribe to new comic releases using the app. This is where the similarities end.