The 50% figure is a pure hardware number. That is, speaking in terms of the raw physical capability of the respective parts, rather than their utilization. That number hasn't (and won't, short of an up-clock) actually changed at all. The number that's changed is how much of the X-Box One GPU is going to be reserved for Kinect and whatever other OS tasks (apparently 10%). At the moment, we do not actually know one way or another what the comparative number on the PS4 is, though open speculation is that it's probably lower to begin with because the console doesn't have a GPU-intensive peripheral built into it.
They X-Box One is only "gaining" GPU power here in comparison to how much it originally had available, whereas it's entirely possible (and likely) that it "loses" yet more in comparison to the PS4 due to the latter likely having a smaller GPU reservation than the One can manage without sacrificing Kinect utility. That's why some people here have consistently been recommending Microsoft's PR should stop making direct comparisons to the PS4: they come out looking a lot better if they just talk about their own system rather than trying to one-up the competition.
As for RAM reservations, both systems already have considerable - probably somewhat excessive, even - amounts of it set aside for OS functionality. The amount chosen was almost certainly greater than will be needed for the sake of future-proofing, and it's quite likely you will see more of it freed up for application use on both systems moving forward as they receive OS optimization. That could be several years down the line, though, as neither company wants to get blindsided by having some hot new app crop up that they want to integrate into their OS only to find out they're short the RAM to run it alongside existing applications.
