For in-app purchases Apple collects their 30%, for Apple Pay substantially less. That’s what this comes down to.

In think it more or less comes down to this: If you buy something you (potentially) use inside the app (an ebook, access to some server-side service you can use with the app, …) it’s an in-app purchase. If what you buy is something you use outside the app (a taxi, a pizza, all physical goods, …) you can use Apple Pay.

This differentiation has always existed. Until now Apple just didn’t offer any help with payment with the second category and you had to do it all on your own.