Arrangements like Apple's and Samsung's may sound strange at first but it happens a lot more than one might think. I work for a very large French company that has its own in-house IT services group, yet my subsidiary handles the majority of its IT operations on its own, including using external hosting companies and service providers that directly compete with them. We can get away with it because we execute faster, with better flexibility, higher quality, and for less money.
BTW, controlling the manufacturing isn't the advantage some make it out to be. It's a very low-margin industry, which is why so much of it is done in low-wage places like China. If bringing manufacturing in-house had strategic value then you can be assured that Apple and any other company with a decent mountain of cash would work on acquiring such capabilities. Take a look at Sony- nobody is citing their in-house manufacturing as a key differentiator or advantage.