I haven't seen a PC game that looks as good as that Killzone demo.
Do you know why you don't see PC games looking like that?
It's because the games are made for console, and the ported to PC.
If you made a game that made use of the full graphics capability of the latest PC hardware, it would be vastly superior to anything you currently see on console, or anything you will see on the Playstation 4.
But, it would also mean that only the people with top of the range PC hardware could run it.
In the Playstation 4 demo, the footage is being played on a PC in the background, a PC with the same spec as the PS4, but a PC all the same.
Now, the release of the PS4 can only be a good thing for PC gamers, as it will mean that developers making cross platform games will not have to dumb down the graphics to cater for out of date console hardware, which will mean the capability of the PC can be utilised more, but given a year and the PC will once again be capable of something vastly superior.
Take for example this image from and Nvidia showcase in 2007:
and compare it to the image from the PS4 demo:
there is not much in it, and that was 6 years ago, see what I mean?