As an Authorized Retailer technician having the back glass be replaceable is so nice. For the older models we just replace the whole frame the glass is attached to rather than only replace the back glass so it makes repairs not only easier but something that can actively be done at our store(as we dont keep frames in stock).
Apple doesn’t process the transaction, a different payment processor does, Apple just provides the API for developers from said payment processors to implement in their app.
The current closest thing for tap to pay for consumer to consumer payments is NameDrop then using Apple Pay Cash through iMessage however this is a less seamless method and is only available in the US. I can however see Apple expanding the tap to airdrop features to Apple Pay Cash in the future, perhaps with iOS 18.