No, but console OSes and Drivers are (well, compared to PC drivers).
There's an enormous amount going on between your code and the metal on a PC, even when writing C++ w/ OpenGL or DirectX. Driver overhead for graphics is HUGE (which is what this is about).
PC hardware comparable to PS3/Xbox360 performs significantly worse under real world conditions due to the way the graphics stack is set up and programmed against. The new Direct3d 12 (as well as AMD's Mantle) are attempts to tackle this.
> PC hardware comparable to PS3/Xbox360 performs significantly worse under real world conditions due to the way the graphics stack is set up and programmed against.
I doubt the significant part. And even if this was true 7 years ago, it's definitely not true now. Comparable hardware would mean something like a GTX 760 (both the PS4's APU and the 760 have around 1800 GFLO/s). That card can do everything current consoles can.
Mantle is for lower end cards anyways, mid tier hardware like the GTX 760 and what's inside current consoles won't see a change that dramatic.
No, Mantle is for lower end CPUs. It's all about reducing the CPU bottleneck to feeding a graphics card effectively.
Which, incidentally, is the reason why the initiative came from AMD (also the strong emphasis on multithreading, since AMD sells cheap 8 core CPUs). If you can all of a sudden game on a weak CPU, then Intel chips will look less attractive in comparison.
Where you're seeing small improvement with higher end cards is that they're pumping the resolution, AA etc, with the same number of draw calls. If you instead ramp the draw calls up - for example by putting a ton more objects in your scene - you'll be able to get much more out of high end cards.
Mantle isn't going to help at all in the move to 4k, but it really will allow for much more complex games on the PC, akin to when Total War was released.
I'd also not take the launch titles as a good indication of what the hardware of these consoles is capable of. They're usually rushed, ported from other platforms, etc. The hardware is capable of much more.
This is a good demo that goes into lots of detail:
