They can sell other places, but not promote those other places within the app.
They could offer their subscription on their web site and collect 100%. Their app would then be required to offer the same subscription deal as an in-app purchase for the same-or-lower price, and then they would collect 70%. The app could not refer users to their web site for purchases.
They could offer their subscription on their web site and collect 100%. Their app would then be required to offer the same subscription deal as an in-app purchase for the same-or-lower price, and then they would collect 70%. The app could not refer users to their web site for purchases.