As much as I believe that Basecamp will do the right thing for their customers the harsh reality is that the vast majority of app developers suck and their subs

As much as I believe that Basecamp will do the right thing for their customers the harsh reality is that the vast majority of app developers suck and their subscription system will end up looking more like: "We accidentally leak your credit card info. We accidentally double charge you. We refuse to cancel your subscription when you want to because you signed a hidden one year contract." Apple's subscription restriction is optimized to prevent the bad actors in the ecosystem from abusing Apple customers. And unfortunately there are a lot more bad actors in the marketplaces than there are good actors who are trying to do the right thing. If it was a perfect system then yes it would be nice for Apple to allow third parties to have their own subscription systems. But I'd rather be locked into Apple subscriptions than deal with the nefarious and poorly implemented custom subscription systems of the average shovelware app developer.