Sony is 'forced' to use an AMD CPU insofar as they're part of the same silicon as the GPU, a combo AMD calls an APU. They're off-the-shelf parts made for notebooks and HTPCs. Cheap, don't draw too much power/produce too much heat, stronger GPU than CPU (with Intel it's the opposite).
I'm still using a Phenom II 965BE. This thing was EoL when I got it and still does good work. I'm going to keep using it just to see for how long it will still serve me. I care about framerates a smidgeon more than the general population, but I don't have to run everything max. So long as I can get a sharp image on 1080p at acceptable framerates I won't need to upgrade.
Same goes for my 280X GPU. That thing was a re-brand from a generation prior. Good enough for 1080p right now, but maybe not too much longer. (The PS4K GPU looks like it might be as, if not more powerful.)
I want to keep the system at least until DX12 games take off, to see how that shakes out with this configuration. Don't feel the need to upgrade otherwise. (Power consumption is a bigger concern, actually.)