Please learn to read more slowly. The changes apply to providing "in app" purchase of "subscriptions". It does not apply to item individual items purchased outside of the app.The relevant change isn't about the subscriptions for Kindle.
It is the fact that any purchased media to be used within the app must now be sold through In App Purchase (for the same price) -as well as- any outside source. That's the issue- can/will Amazon afford to give up already razor thin margins to give 30% to Apple? Probably not.
Please correct me if I am wrong by providing the proper citation.