Patreon probably gets by because a lot of Patreon rewards are physical items, or other services performed by the creator where Patreon (and by extension Apple) cannot guarantee will be received.
Meanwhile an app whose subscription model is “you get access to digital content” falls square within Apple’s IAP rules. I’m rather shocked Fanhouse got approved in the first place.
The fact that Fanhouse got approved means Apple's rules are arbitrary.
Not so arbitrary. If you are big and in the market Apple is not interested in, you are safe. Once Apple wants to step into that market, you should be careful (ex: spotify).