EatChildren, one thing I have noticed after following all this quite extensively is there are three distinct versions of Dark Souls 2 that have been shown to the public.
The vertical slice is just that, a vertical slice of gameplay that was created to show off the game. It has completely different geometry and textures from the other two versions, but has the same lighting effects and darkness mechanic that we see in the PC version.
Its obvious that From did use assets and general level design from this vertical slice for the final PC and console versions though.
The PC version is identical to the console retail version in geometry and textures, but with a few exceptions. Higher resolution/frame rate, high-resolution textures, more particle effects, better lighting, and the darkness mechanic.
My hypothesis, From wasn't lying when they said that the PC was lead platform and the engine was developed for PC/next-gen.
All of these graphical effects and features were stripped from the PC version for performance reasons on consoles. From needs the extra 6 weeks to finalize all the extra effects for the PC version.
Its also a win/win for Bandai as they will secure the key 'double-dipper' demographic for the PC version as it is considerably better in performance and graphical effects.
If you are interested, I posted a more in-depth analysis
here.
Screenshots taken from the PC trailer:
http://i2.minus.com/idQf74JSP5NiF.jpg