Long ago, in a galaxy far, far away, there was a site called 'skinz.org' which instigated controls over wallpaper submissions in an attempt to control/limit the size of the Wallpaper section on what was/is specifically a skin site. Walls were seen as an adjunct to the skin sections, not the 'prime directive'.
The only way to limit, or moderate these wall submissions was to make a 'qualitative' judgement as to their 'uniqueness, innovation, or adept artistic skill'.
Blue Swirlies, lens-flares and other 'filter-frenzies' became the criteria for immediate rejection, unless there was a fantastically original slant on their use.
Now, with the plethora of 'XP' related submissions as well, critical mass can be reached, whereby there are just too many closely related walls and/or skins to justify inclusion on those grounds alone.
I clearly remember Shoggot at skinz copping a lot of flack from disgruntled artists, but ultimately it resulted in a quality collection of works.
So many sites exist specifically for walls and without any controls on uploads, and these are swamped by 'a lot of the same'.
Here, at WinCustomize, we are endeavouring to just raise the bar a little....