Cases may let us mix up what our iPads look like on the outside, but to keep things fresh and fun on the inside, we need awesome iPad wallpapers for the Lock screen and Home screen. And we need them in Retina display resolution (that's 2042x2042 in this case -- needs to be rotatable). Sure, Apple provides a lot of really high quality, really beautiful looking wallpapers built right in, but for some of us, there are never enough.
Apple's also tend to focus on nature and texture, which is great (the new ones released in iOS 5 are all water-themed). But some people prefer more tech-styled, electronic wallpapers. Some prefer photos of family or friends, or favorite movies, TV shows, or musicians. Some even like their iPad wallpapers a little more naughty than nice (hey, we're not here to judge!)