This article is a good take on the motives of why Amazon– who already has your REAL credit cards directly connected into it’s ecosystem — would need to mint it’s own a virtual currency in “Amazon Coins.”
Basically it’s all about mobile devices. And it’s the same reason that airlines do frequent flyer miles. In an Android platform, they need a loyalty program to keep distinguishing Kindle Fire platform from every other Android device.
via Why Amazon wants its own currency | The Verge.