Just like the default iPad wallpaper comes from a real lake called Pyramid Lake (which is supposed to be in Nevada, though I'm sure I pass signs for it every time I drive up to San Fran from here in LA), so too is the default Lion wallpaper based on a real picture of a real galaxy, specifically the Andromeda Galaxy. Boing Boing found a real image of the galaxy taken by astrophotographer Robert Gendler, and when it lined up the Lion image with the real thing, it found that Apple actually deleted a few stars and galaxies from the sky, just for Lion.
Don't worry -- Apple didn't actually delete the real stars (though with its market value, it could probably at least put a dent in them). Obviously, it was just a Photoshop job to make the wallpaper a little smoother and more pleasing to the eye.
But it is interesting that someone at Apple said, "You know, if that star weren't there, the universe would actually look a lot better!" What if we did have a universe designed by Cupertino?