But there is no case where it should be up to a web app whether its content should count as background audio. It is possible that a user should be able to flag

But there is no case where it should be up to a web app whether its content should count as background audio. It is possible that a user should be able to flag such a situation, but native apps both have affirmative consent when downloading an application and have permissions models the user can manage, whereas the web has neither and web browsers need to assume both malicious and incompetent web devs will do terrible things with any feature they allow.