From Jamie Hall Blog - http://ninjamoomin.seshn.com/xbox-one-where-it-all-went-wrong-and-how-microsoft-ignored-the-warning-signs-2
Sometime just before February 21st 2013, the game may already have been over. A battle lost on something as simple as RAM chips, with Microsoft subsequently alienating it’s customers to bang the nails into Xbox One’s coffin in the months that followed. The miss-reading of their customer base has been, in short, staggering. ---
All of that could have been prevented had Microsoft simply dialled into the audience that made Xbox a viable console to begin with – the core gamer. Microsoft gambled for a broader audience with Xbox One, in the process forgetting that the early adopters (and most vocal advocates) in the console market were the people who played games, not the wider audience that might use the system to watch Netflix on the TV. Ironically, it may simply have been that Microsoft’s vision was indeed grander, but ultimately that cost them dearly. ...
Xbox One simply had less room on the chip for graphics processing elements and the dual-memory set up was something developers would need to spend time learning and optimising.
GDDR5 is very fast ram. Until Mark Cerny announced the final amount in the console, most developers had been told to expect 4GB of system memory. However Sony, in essence, lucked out.
When higher density GDDR5 chips became available, all the console maker had to do was swap one set of chips for another in its design – instantly giving PS4 a large, single pool of high speed memory to feed its graphics processor. This set up is easier to program than Xbox One – meaning developers can spend more time on things that make a difference to the ‘feel’ of a game rather than simply getting it running to begin with.
This advantage is compounded by the PS4’s GDDR5 memory not taking up space on the graphics chip – meaning for a similar silicon die size and cost, Sony can dedicate more real estate to graphics. ---
Even if the price of the Xbox is cut to match PS4’s $399, the console is simply not as powerful. PS4 has a qualitative advantage that the most vocal parts of the audience are very warm to. Even with this change, Sony still has the option of selling at a higher price due to the tangible advantage it can point to in the gaming space, or simply stomaching a much smaller cut and still being both cheaper and more powerful. If Microsoft take out the Kinect Sensor (which has yet to prove it’s worth to gamers) then it loses the only point of differentiation beyond what’s under the hood.