Let's not forget that Sony is allowing developers to access lower level of hardware coding.
"Using a DX11.1+ feature set, developers are able to use many of the same tools used to program PC titles but also have additional debugging tools and low level access to the hardware. A new low level API below DirectX, but above the driver level gives developers deeper access to the shader pipeline."
http://www.pcper.com/news/General-Tech/GDC-2013-Sony-Reveals-Additional-Details-About-PS4-Hardware
Low-level access and the "wrapper" graphics API
In terms of rendering, there was some interesting news. Norden pointed out one of the principal weaknesses of DirectX 11 and OpenGL - they need to service a vast array of different hardware. The advantage of PlayStation 4 is that it's a fixed hardware platform, meaning that the specifics of the tech can be addressed directly. (It's worth pointing out at this point that the next-gen Xbox has hardware-specific extensions on top of the standard DX11 API.)
"We can significantly enhance performance by bypassing a lot of the artificial DirectX limitations and bottlenecks that are imposed so DirectX can work across a wide range of hardware," he revealed.
The development environment is designed to be flexible enough to get code up and running quickly, but offering the option for the more adventurous developers to get more out of the platform. To that end, PlayStation 4 has two rendering APIs.
"One of them is the absolute low-level API, you're talking directly to the hardware. It's used to draw the static RAM buffers and feed them directly to the GPU," Norden shared. "It's much, much lower level than you're used to with DirectX or OpenGL but it's not quite at the driver level. It's very similar if you've programmed PS3 or PS Vita, very similar to those graphics libraries."
http://www.eurogamer.net/articles/digitalfoundry-inside-playstation-4
You cannot just look at the hardware and ignore how developers will code for the console (PS3 was the perfect example of this). This means even if Xbox next matches PS4's specs exactly, PS4 will still perform faster due to developers having access to lower hardware level.
Looks like Sony is doubling up against MS: rumoured faster hardware and superior/more efficient access to hardware coding that goes lower than standard DX11, which will allow developers to extract more power than the theoretical performance of a Desktop HD7850 2GB operating in a standard DX11.1 environment.
