"3.1.3(a) “Reader” Apps: Apps may allow a user to access previously purchased content or content subscriptions (specifically: magazines, newspapers, books, audio, music, and video). Reader apps may offer account creation for free tiers, and account management functionality for existing customers."
It isn't because Netflix or Amazon are "powerful" enough, but that they saw that these were traditional multiplatform services.
I disagree with the ridiculous Hey situation (and note that Apple backed down), however let's be accurate.