If the bottleneck is the CPU then this make a lot of sense. The component that is nearly the same in both the PS4 and the XB1 is the CPU. The extra GPU power and memory in the PS4 don't matter if they are not involved in the bottleneck. Sounds reasonable to me.
That's not how it works, though. Vertex data is fed from the CPU into the GPU. Then the GPU does goofy math over every point on the screen and renders out what thing it hit, over many times.
Okay, let's try an analogy.
Once the GPU has the scene data to work with, it renders the game at any resolution it wants. Just imagine it like an autistic kid, sitting behind a screen door looking out towards the street.
The CPU is the puppeteer, making the street. The porch. The cars driving by. Sets all of that up.
The GPU is the kid looking into each square in the screen door and saying what color he sees when he looks in it.
If it's a tighter screen door, with smaller holes, it doesn't affect how detailed the street is, just how many holes there are, and how long it takes to do it.
The PS4 kid can count 30 holes in the time it takes the XB1 kid to count 20 holes.
So no matter what happens, the PS4 kid can count more holes. And if they're limiting it to 900 holes because of the puppeteer in the street, that makes no fucking sense, does it?