then it's even worse for Sony.

Not necessarily. The decision did come "last minute" to go 4GBit. Probably Hynix offered them a "good upgrade deal" on the chips (I assume H5GC4H24MFR-T3C are the (cheaper model) chips they're using). And these 4GBit chips probably are the new "work horses" as graphics memory seems to be generally doubling on the pc side. Still way more expensive than DDR3 or DDR4 but MS isn't really decisively cheaper with dedicated large eDram.

But you are forgetting that most of those graphics cards use 1 or 2 GB, while the PS4 and the Nextbox (if the rumor is true) will use 8 GB.

Sure, they won't sell as many consoles as graphics cards, but each console sports 4x times as much RAM than a graphics card, so they will have an impact on the production of GDDR5 RAM, hopefully a good one.

Those Numbers also don't include FireGL or Tesla or Quadro or the various Notebooks that have GDDR5 Ram either, it's at-least double that number and maybe even triple if one is to be optimistic.

Sony would have also been stockpiling for months.