Exactly. That means that an app that wants to offer a "rental" can continue to do so via an in-app link to another purchase process, and does not need to offer

Exactly. That means that an app that wants to offer a "rental" can continue to do so via an in-app link to another purchase process, and does not need to offer the same service (for the same price) in a way that Apple can get 30%. The value proposition is pretty similar. Let's be honest. The chance that a kindle book is going to still work in 100 years is vanishingly slim. Might be unworkable marketing-wise, though.