It doesn't matter that they control when to announce the products, because demand is always going to outstrip supply for a new iPhone during launch. It doesn't make sense for them to have a production capacity of 100 million iPhones just for the launch quarter when they only move 50 to 60 million in the succeeding quarters.
Look the poster you are replying to has far better supply chain experience and superior business acumen to that of Tim Cook. Who are we to question him?