Interesting. Per [1] they can't be cashed out or exchanged. So you buy coins, that's the transaction. Amazon is probably then free to do whatever they want with the money. Their only obligation is to later pay out to developers who receive coins as payment. So they're frontloading their earnings. And devs only receive 70% as usual so Amazon gets 30% totally in the clear (no potential future obligations).

[1] http://www.digitaltrends.com/mobile/heads-or-tails-amazon-co...