It is but not as much as some users in here are claiming. 

Well, the differences in the systems seem pretty clear cut to me. From the into that's been revealed, they both use PC architecture, and their specs are basically identical, but the ps4 has gddr5 RAM and a superior GPU. We also know that BF4(and most games, really) is largely GPU reliant, at least on PC. Based on that info, its safe to assume that the performance differences we see with BF4 at the very least are thanks to the PS4's GPU and RAM advantage, right? You say that games will become even more GPU dependant in the future, but what is it that you base this assumption on? Exactly what kind of games are going to showcase this gap increase? Physics heavy? Open world?

As for Dev tools/ working environment, it's hard to know much. Going back to the bf4 example, though, I think based on the issues the game had, it was probably rushed, developed with early hardware and immature Dev tools. That affects both consoles, though, and ( based on rumors , yes) the One's tools were apparently less mature than the ps4's anyway.

The difference in hardware on paper is the clear cut part. Games are not created equal. Some games require more of the CPU. Some require more of the GPU. Some games need a lot of RAM and others don't. As the GPU of the PS4 is obviously better, any games that make more use of it will show larger differences on the PS4. These differences will not be linear. They will be exponential. Not significantly so but exponential nonetheless.

Note how PS3 and 360 multiplatform games were largely even for the first few years. Heck, some games ran better on the 360. As time went on it was noted that PS3 multiplatform games were popping up that were running better. Games like Dragon Age: Origins for example. So why did these games go from being pretty much even to having some noticeable differences even if they weren't night and day? If it's linear then it should not have happened that way but it did. That means that as time went on the hardware in the 360 struggled to keep up with certain multiplatform games, especially as developers started figuring out ways to make the PS3 hardware work better than they did early on.

No one has tapped these machines yet and it's obvious that the ceiling is higher for the PS4 so as developers dig in you'll notice the difference grow. Will it be by such a margin that the X1 looks like a joke? No. Not at all. X1 multiplatform games will be competitive in the performance and/or looks department for the entirety of the generation. They will just not be as good. Some games will be a lot closer. Games that don't put as much emphasis on the GPU. The reason I say the GPU will become more important over time is because the CPUs of both of these consoles are nothing impressive besides the number of cores they have. The GPU is the biggest difference between these machines so as the CPUs get loaded down they will have to make use of the GPU to offset.

So basically, the higher performance ceiling of the PS4 coupled with the fact that this performance ceiling is based on components that are a mixture of even and superior to the X1 while developers find ways to get more out of what they have in front of them makes it likely that at some point the gap will grow and not simply remain equal. 

According to some users its a bigger disparity than Original Xbox and PS2. :-p

Story telling cinematic action/adventure game doesn't need 60FPS and will not be good if its.