given their history with paying developers that are the app of the day on their store[1], I can see them finding a loophole to avoid paying devs who collect payments with coins.
[1] http://blog.shiftyjelly.com/2011/08/02/amazon-app-store-rott...
[1] http://blog.shiftyjelly.com/2011/08/02/amazon-app-store-rott...
It seems like that's a major part of this push - if you want to receive any of these free Amazon dollars, submit to the app store.
In this situation they are claiming that it's exactly the same as cash to developers - that is, you will receive 70% of the purchase price. I have absolutely no reason to believe that they're attempting to mislead or be dishonest.