I think the main reason we're not seeing the PS4 pull ahead as much as it should, is because of the developers, but it's for a very innocent and honest reason. Nothing sinister.
They're most likely trying to improve their weakest link. The weakest link is the Xbox One in this case, so they spend most of their efforts there.
For example, if they set themselves the target of 1080p 60fps, then they'll try to hit that on both platforms. The PS4 gets there quite easily, and they don't need to do much more after that point. So now they focus more of their time and resources getting the worst-looking/performing Xbox One version up to snuff.
Your worst result is what stands out. So it would be more beneficial to have both versions look good, rather than have one look great and the other one bad.
"Never argue with stupid people. They will drag you down to their level and then beat you with experience."
-Samuel Clemens
