Still, you do raise a good point - that S3 bucket is owned by the app, not the user. But it doesn’t have to be this way forever, and AWS is an Amazon product. Amazon has the credit card information of nearly everyone in the world. I would not be surprised if in the future, we see a sort of federated model, where users of an app pay for their own storage at S3 by linking their Amazon account. The app would be like a reseller/affiliate of Amazon, and could pass storage costs directly onto their users without worrying about complexities like pricing tiers to account for variable customer requirements.