It's important to distinguish that this is GDDR RAM not plain DDR. Although nowadays they're pretty interchangable, GDDR is built with Graphics chips in mind and will operate better in a graphics context.
Whereas DDR is more adaptable and can qork quickly in a much more generic concept.
I believe the idea behind this is Microsoft's view to being an all in one entertainment system, not a gaming console. Microsoft will more than likely lose some bandwidth due to it being plain DDR, however, until the technical specs are release this is all speculatory.
AFAIK, the XBox runs on a custom built 8-core AMD processor that incorporates a graphics chip. If this is true, the memory controller on-chip may have been built to be just as efficient with DDR3 as the PS4's GDDR5 (I doubt this though).
Having owned a PS3, I'm not going to be looking for a PS4. The PS3 was buggy and the console is slow and laggy. Not even Fifa 12 could run at 60fps (not to mention the controller lag)
So I will be getting the new XBox One.
The ability to run the same code on XBox as your PC is going to be a bit of a game changer in terms of development methinks =)