According to their official website. At least from what I understand, they are improving graphics in the actual game, not just trailers and in-game video.
You can pre-order it here on Amazon along with Halo 4 (very easy):
There is some nifty code that I copied below, it didn’t work on my page, but for any web-wizards out there, it looks like they took two separate images and display them together somehow:
<div><li style=”position: absolute; top: 0px;” data-title=”Pillar of Autumn 1″ data-image1=”http://nxeassets.xbox.com/shaxam/0201/18/f1/18f1424e-e1bc-4ede-8d80-152d169def78.JPG?v=1#slide-1-new.JPG” data-image2=”http://nxeassets.xbox.com/shaxam/0201/5c/9b/5c9b70a0-a909-4a96-80c8-f1f1a99dc883.JPG?v=1#slide-1-old.JPG”>
Here are the actual images and a screenshot from the actual page so you can see what the site looks like: