I think the Apple case and this one is a horrific lint/dirt trap...all the lint/dirt between the case and your iPhone is like a grain of sand in your eye...
You ever had to remove those chromed plastic emblems from a car? They're attached with some crazy 3M foam adhesive? Well once you remove them, the dirt and debris that gets trapped there through time acts like sandpaper that constantly rubs (car vibrates) away at the clear coat and paint. You literally have an etched outline of the emblem into the paint that you can't polish out with compound..you literally have to sand the entire surface and repaint to remove the etch and pitting.....same analogy.
My old 3GS' back was riddled with pitting and scratches with typical hard plastic snap-in type AND soft TPU or silicone cases. Thus I stick with bumper style with skins