The website is called Ubuntu Gallery and according to the editor John, the purpose "was"...
"The purpose of this site is to show case illustrations submitted to Ubuntu and the greater community as wallpapers targeted to the 11.04 release referred to as Natty..."
Although when having a look at the archive ... before the 11.04 was released the site received a lot of wallpapers by various artists but after the launch... well there is certainly a bit of a shortage of new-wallpapers.
Anyhow, as said... why not make this already cool looking site a "major" wallpaper center for the ones with the talent and for the enjoyment of the ones like me who has not talent at all :) + an "epicenter" for "Ubuntu art" for the upcoming releases! (well, I think it kinda happening already :D).