Isn't he lying btw? A 680GTX is not double the real-life performance as a Radeon 7850 (which is similar to PS4's GPU).

They already did, a lot of phones and tablets use them.....

depends on the situation but he's wrong for the most part, I'd put it at about 65% of a GTX 680.

yeah but that's also the advantage of consoles and why I buy them.  You don't have to adjust settings because the game has been made to play on that system.  They are optimized to handle whatever comes out for the next 10 years because developers only have to make games for 1 setup.  Plug in and play is still a very nice feature for consoles and PS4 will better than 3 in this regard because of faster/background patching and updating.

No, but you can get a 6gb Radeon 7970, kinda makes having 4gb pointless. :P

Does Nvidia have anything similar to the APUs ?  

Yes.
nVidia Tegra, however it's targeted at the ultra low-power market. Aka. Tablets and Phones.
However, it's not far-fetched to say they couldn't engineer say... A Geforce 660/670 with a 16 Core (Or more) ARM processor all in one package to drop into a console.
Just unfortunatly the CPU performance of ARM chips leaves much to be desired as they have an even lower IPC per core than Intels Atom, which AMD's Jaguar leaves both in the dust due to it's OOO design.

Isn't Tegra a line of GPUs for mobile devices ? 

It's a CPU and GPU and chipsets aswell as other logic all on the same die. Aka. SoC or "System on a Chip".
AMD's APU's are essentially the same without the chipset and other logic and uses a CISC x86 for the processor.

This has always been the case though. Fishy timing nVidia...