Similar tech, but watered down... which is what they do for mobile series chips.
The APU or Fusion technology always has AMDs equivalent mobile tech. Thats how they get the size and power requirements.
So yes, the APU in the PS4 is the graphical technology equivalent of a HD77XX or HD77XX, but it would have the "M" moniker at the end of the label to denote that it is the mobile series variant.
This is why Nvidia is saying its a low/mid end GPU yet we know its based on a HD7XXX chip. Its a HD7XXXM GPU.
My $700 PC runs a 7850 with a 3470 intel CPU. Both much better than what's on the PS4 then. So it doesn't need to be a $1200 computer. You can do the PS4 specs for $400, I guess.