I see the Apple watch as a companion and would even prefer that most of it's functions stay on the phone.
Even if compass and GPS data comes from the phone, native Apps would still benefit. Right now the user interaction is transmitted from the phone App to the watch to be displayed and acted upon.
Once the user interaction is running natively on the watch, the phone dependency could be beneficial because you could define what data is transferred and how it is interpreted by the native watch app.
In short: Once the Watch App part gets to execute code, the phone as a data provider and storage device is even more interesting than today.