You also have to remember:
In desktop computers the GPU in the APU is pretty much limited by the ram. So there is no real reason to put a strong GPU in it (the GPUs in the A10 still are totally ram-limited in most cases).
For consoles you can design the GPU around the available ram (that's also one point you may change in your opening posts: just because all rumored GPUs use GDDR5 that doesn't mean anything on the matter which kind of ram the consoles will use. There's no real problem using DDR3 if you have a large enough bus width). Ram in PCs is (usually) limited to dual channel, but in a console you can run as many ram chips parallel as you want.
AMD could design a special GPU for PS4s APU which can be a lot more powerful than the 7660D.
