For once I agree with you. The idea of having both platforms have the same games is dumb.
It's not "dumb", there's some merit to it, it's just if both the handheld and console variant are fairly close in horsepower, then it becomes a question of really what's the point?
You may as well have one variant that can do both and as such increase its novelty/appeal factor. You can't exactly play your PS4 and then throw it into your bag and play it on the train too. That would be one fairly large differniator for NX. Throw in some kind of gimmick novelty controller, and voila you've probably got something that is sufficiently "different" from other game systems.
Not saying this is a good (or bad) idea, just that there is some logic behind it and it probably meets certain tent pole's that Nintendo has. It has to be different from other game playing devices.