Maps are operating system features that any application can rely on being present. Their are OS APIs that require that the mapping infrastructure be present.
Can't the APIs stay constant while the supplied data/backend gets changed? After all, isn't that the whole point of having a public API so that the implementation can be changed without changing the calling apps?
They could, but Core Location in iOS 6 uses the backend data for things like getting your car route. If I recall correctly Google doesn't let you use their api for things like that.
Basically removing the Maps app is one thing, removing new OS features that use the same frameworks is another.
That is what I said. My point being removing/adding Apple Maps isn't the hard part, it was merely to point out that there is more to the mapping api's than an application. And if legally Apple cannot do turn by turn using Google apis, then they cannot provide one to one compatible api's with both. So they just dropped the Google api backended MapKit.