This 'story' has been floating around for a while... here's the deal:
The PS4 architecture is really straight forward in terms of hardware; eg. a powerful individual GPU interacting with the CPU. The reason there are all of these '50% more powerful' claims is because the hardware layout for the XB1 is more complicated; eg. the GPU is supported by the eSRAM to boost speed.
The effect of the eSRAM on the XB1 is the big unknown, and while there's no doubt the PS4 has superior hardware (on paper at least), it's unlikely that the difference will be the 50% as claimed. (To think that both Sony and Microsoft weren't acutely aware of exactly what the other was developing would be naive.)
It's also little unfair to attribute Valve's 'it's too hard' statement when comparing the XB1 architecture with PS3's infamous cell processor; every anonymous developer would know this...
So, getting back to your question about the graphic drivers!
The final specs for the hardware of the XB1 were only recently finalised; during the early Durango test kit days (when these rumors first started appearing), the graphic drivers weren't optimised for eSRAM at all. However, this changed ages ago. Developers have been well aware of the eSRAM for a long time now; the final driver tweaks shouldn't make or break the development of a game - think of how AMD and NVIDIA can update driver specs after the release of a game to improve performance without code having to be changed.