Most of those are not retina size 2048x1536, which I think is what the poster was looking for.Google "iPad Wallpaper"
What's the big whoop?
I'll do it for you...
Mine is not distorted, cropped, but so is 2048x2048.The ideal retina wallpaper size is actually 2048x2048. At this resolution, the image isn't distorted when you switch from landscape to portrait orientation.