Ultimately, we're talking about a 3gb texture which can be very high quality or meh quality, and using tiles to keep the most in view things higher res without wasting all the bandwidth. It will still save craptons of bandwidth and allow far higher quality texture usage on the PS4 so esram or not is fairly irrelevant to the discussion as on the PS4 tiling can lead to massive increase in texture quality.
As luggles said, in the DX api it requires DX11.2, in any other API it doesn't, even more importantly is API's on the PC are a standard and take into account a lot of hardware and put in limits. One of the reasons for Mantle is there are many short cuts, accelerations and optimisations that simply aren't exposed via DX, or openGL. Quite a good youtube vid of the Oxide dev's basically saying DX is so so slow to add these features after they are wanted and supported.
On a console, Sony control the API, if the hardware can do it, they can support it. Doesn't mean they always will because the hardware may support some insane feature they'd love to add but simply don't have the power to use so would be a waste to make it work. But consoles and low level api's basically don't have this API limit. They don't have a choice of openGL 4.2/dx11.2 and if they don't support something they simply can't do it. Having control of the API means you can do what you want with it. GPu's on PC's have been locked in to what are incredibly slow to respond API's which aren't controlled by game dev's nor gpu makers. When you can control the API and add whatever you can, so much more is possible.
Ultimately The es ram might help, but the esram helps accelerate some stuff, it's still got a crapload of stuff to load from system memory for each frame as well which will be vastly slower.
Neither is really "better". The ddr3 +esram might save some power, means a bigger die size and higher cost though. Ultimately it will be faster at one thing and much slower at another.
The key is tiling reduces the bandwidth required full stop, it prevents needless waste, and that will be the case on either console. Coding to include esram and limit texture sizes to be very specific is a heck of a lot more work and more difficult. PS4 will be easier to code for and ultimately easier to optimise.