Apple‘s design goal is to create holistic and consistent experiences. Apple focuses exclusively on devices and services that they can control. In fact, this control actually has likely increased as Walt Mossberg writes about WWDC 2014 on re/code.
Customers are being enticed more and more to stay within the Apple ecosystem (ideally with more iDevices down the road). However, TouchID will make this holistic experience even more convenient, stickier if you like.