They are talking about rendering and high end PC. I never heard about 3D rendering on CPU or devs optimizing the game on PC for single core 3GHZ CPU.

The preceding sentence in the article says they're talking about both CPU and GPU.

No, they are ASKED if it's challenging about CPU threads and GPU computer units, and they ANSWER only about rendering, so on GPU, so it seems they have no problem with multi thread on CPU (that's second year IT student stuff, on a bigger scale, but still, and they do have to do it on pc too anyway, 4 threads is the standard now) or minors one, and bigger problems with the GPU's 18 CUs, wich is totally understandable.

They said "cores" not "compute units".

Games are already programming for multiple cores - it's not like every 360 game used only 1 of its cores.Read closer what was said:

"It’s been challenging splitting the renderer further across threads in an even more fine-grained manner – even splitting already-small tasks into 2-3ms chunks."

Splitting it FURTHER. It's already split. Multi core PCs will generally have cores of 2.33-3+ Ghz functioning. PS4 is what, 1.6ghz? Some tasks naturally lend themselves to being split off, and some tasks lend themselves to being on a single core. The issue is that tasks which heavily favor being on a single core suddenly need to be split as well.

yes, slow clock speed are common on all 3 new gen systems, thats going to be a problem with the devs that worked with ps3 and x360, they say the same on the wiiu front, they have to accomodate to this "new" console tech, GPGPU is the "new" frontier. And yeah ps4 have an awfull slow cpu ;) just like xbone and wiiu.

LOL most those guys would have finished their IT education before it was second year stuff at school. Courses evolve with technology and game developers also have to otherwise they will fall behind and become insignificant.

Of course they need to adapt permanently. Imagine a doctor using 50's medical knowledge to treat you, that would be unthinkable. That's just one of these jobs where you can't just live in a cave and expect nothing to change.

This. While multiuser, multitasking and DSP (including graphics) mainstream applications and supercomputing ones started using available parallelism quite early, single user mainstream SW, including games, often hogged single core's power, but almost always lagged behind what HW offered in terms of parallel computing power, and this affects games the most, as they need most of the computing power available on a machine, and outside of easily parallelisable tasks as graphics, the performance of a single core can still be a bottleneck for intrinsicly serial tasks. Better libraries and dev tools can help, developers learning to identify and reduce intrinsicly serial parts to the bare minimum can help even more. For some AI parts, using fuzzy logic and devising AI that can work on partial data, to reduce mutual dependencies, could help too, while mission and quest files could specify when conditions must be met more strictly for the correct advancement of plots, missions and quests.