Apple has been doing this with other APIs for a while. If your app links to a way of signing up for an account that could be used to pay for something you'll be rejected. If you mention the existence of such an account you'll probably be rejected.
Personally I don't like being treated like this - as a user or a developer. So I take my time and money elsewhere.
Personally I don't like being treated like this - as a user or a developer. So I take my time and money elsewhere.