It isn't completely a cost center as they do make money from developer subscriptions. More than the developer subscriptions, they make money by having an attra

It isn't completely a cost center as they do make money from developer subscriptions. More than the developer subscriptions, they make money by having an attractive platform by making sure developers are happy to develop for their platform. "Here's a free shiny shovel that works great!" I think the subscriptions are mostly a small barrier to entry so that not everybody and their grandmother get their own license. For example, if licenses were free, it'd be much easier to share and install open-source software, bypassing completely the App Store. As it is, you'd need to save $99 in apps before it's useful.