All 5 app stores have centralized payment card management. Every app I buy charges the same card. I remove that card, it disappears on all stores. A payment fails on one App Store, I get asked to verify my payment info on all other stores.
I assume purchase notifications come from the same email. You manage your account on the same web UI.
All app stores are the same, but of course you need a different UI and possibly backend. In fact, don't I buy apple watch apps from iOS? Aren't there universal iPad/iOS apps?
Sometimes it feels like the level of conversation at these companies is below high school level.