I'm sure one could brook an argument for desktops being art, but technically, wallpapers are just photos cropped so they'll fit on your desktop and sometimes oriented to the right to make way for icons. Seldom is the person who makes a wallpaper, the actual artist or photographer.
I don't think it's all bad, really. Most of the time, we don't draw or create art with a person's desktop in mind. I could easily do it myself, but 100% of the time I'll go looking for the wallpaper version of the image I want for my desktop on the internet. Someone's got to do it.
I do the same and there's plenty of websites that do it, sad thing is this category is all pretty much stolen art or pics made into wallpaper. I mean how artistic is that? The original intent was for artists to release their own wallpapers or produce original wallpaper. I just don't see that here.