Okay. Let's actually address this logically.I feel it's a legitimate concern. Considering a PC several times more powerful than last-gen consoles struggles to hold a constant 120fps with last-gen titles at 1080p, I don't know how the PS4 would do it with games with any kind of graphical complexity. I'm not rooting against Sony - hell, I just bought a PS4 last week, I want this to take off - but I really hope it's a great showing because it's an important one.
Firstly it's not 120Hz, maybe one day, maybe even with Rift CV1, but we don't know that, the best suggestion so far is 95Hz, because they plan to meet or exceed the Valve prototype.
It is 1080p, and it is 3D, so that's more demanding still, typically from between 30 and 50%.
So let's say it's 1080p+50% for 3D and 90Hz.
That is roughly twice the performance of 1080p/60fps/2D, which PS4 is comfortably providing with very pretty results.
Roughly halving performance seems brutal on the face of it, but then you have to look at what is more effective in VR. Valve have said shaders look horrible, and textures can look really bad, preferences seem to be more flat shading with nice lighting. Ironically, less is more in VR, which bodes extremely well. The other thing to consider is the limitations of game design in VR, you want a very stable simulation, so performance spikes don't happen, you don't want TitanFall where performance demand per frame is incredibly wide, you want a highly controlled simulation, this is excellent for performance.
You're going to see a visual hit, no question, but it's going to be so much closer than you'd expect on the face of it, and the impact of VR is really impressive.
If you have a really beautiful PC, you're going to have a better experience with the Rift, no doubt. But people are really going to be awestruck by what's capable on lower end hardware like PS4.