Like another man who has done such fine work for Blizzard, Mathias Verhasselt, Chris Thunig is here for one reason and one reason only: his amazing landscape paintings for Diablo III, StarCraft II and World of Warcraft.
Thunig specialises in matte paintings, which are static, highly-detailed images used in the background of things like movies or, in this case, cinematic trailers. That's why they look so damn good: they have to pass for the real thing, when the real thing is just too expensive/impossible.
In addition to the matte paintings, Thunig also did some concept work for Blizzard, and you'll find some of his Diablo III paintings and sketches in the gallery above as well.
If you want to see more of Chris' stuff, which he's done for some pretty major motion pictures, check out his personal site.
To see the larger pics in all their glory (or so you can save them as wallpaper), right-click on the "expand" icon on the main image above and select "open in new tab".