YouTube has negotiated a deal that allows this, as did Amazon Video and a few others. Only huge companies can do this, which further makes the argument that what Apple is doing is abusive.
This is not true. There is no rule that states you must offer the same price when signing up if your service is multi platform. The rules only state you can’t discourage In-App purchase. I use several services where I signed up on the website because it was substantially cheaper than in-app.