Physical stores are fine because they have employees, rent, utilities and taxes that are inextricable from each location. Cloudbursting store infrastructure has no employees after some initial devops infrastructure is coded. It bursts on activity. No taxes, no employees. Just giving money to Apple because reasons. Same is true for all digital stores. Steam does a little more to earn it but I think it's too much as well.
Why do you think Apple, Google, etc are entitled to this money? They are swimming in cash. I'm a developer, I don't think you all realize how incredibly cheap it is to scale. Netflix will intentionally brick one of their major data centers to test how well it automatically recovers. Software is going to become ubiquitous with everything, the idea that 1 company just takes 30% is an astoundingly horrible idea.
Has anyone considered that physical stores work on a percentage because they can't cost remove certain expenses like salary, taxes, utilities and rent? Instead think of it as a utility where a store front should operate based on usage, eg data used for downloads, updates, and advertising in charts, and that operational expense should be the baseline charge rate with a 10% profit margin permitted. Apple and Google would hate this because they wouldn't get hundreds of billions of free cash over years. This model could have incentives where cost reduction via innovation can be added to the 10% margin - regulated capitalism keeps competition innovating so that both businesses and consumers benefit.