Android applications purchased in Amazon's app store (which may finally go live to consumers any time now) will use Amazon's special sauce of digital locker/digital rights management to help combat piracy. Amazon spells it out in its developer blog:
The tl;dr version: You can use apps purchased from Amazon on multiple devices just fine; you'll just need Amazon's app store app installed for them to work. It's not nearly as scary as some would have you believe, and it's an extra cushion for developers. [Amazon Developer Blog]
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