They can charge whatever they want as long as they give developers the alternative to use a different payment provider. See Discussions around exemptions for Netflix for instance.
Netflix is exempted from mandatory usage of Apple's payment platform. OP stated that Apple is threatening to pull the app if she does the same thing that Netflix gets away with: avoid using Apple's payment platform, and set up payments outside of the app. For a company that loves demanding its partners adopt Most-Favored Nation clauses, Apple sure does hate treating its app developers the same.
They are allowed to take payment on their website for a subscription, but so is any other developer.
No, they are not. That was what the whole Hey debacle was about. Netflix and Spotify have special privileges there.
the replies to your comments are literally telling you the true story, at least do your own homework
I did however download the Hey app and try to sign up for a paid account, which you can't do.
I downloaded Fanhouse and tried to view some profiles. It says "Follow to see more" but there's no way to follow anyone in the iOS app. I can see this running afoul of some App Store guidelines since you're advertising a feature with no way to use it.
This could be Apple being unreasonable, but it could also just be a misunderstanding of how the App Store review process works. I don't know how long they've been going back and forth with Apple on this.