I was looking at the WoTLK website this morning and noticed that the 4 wallpapers filenames were listed as 1 through 8. Renamed a couple url's and found some wallpapers I don't believe were released on the website. Please correct me if I'm wrong.
http://www.worldofwarcraft.com/wrath/wallpapers.xml
The following wallpapers aren't linked to on the wallpaper page: