I had noticed a few very, very faint scratches on the front of my iPhone that were visible only in bright sunlight. After reading this article, however, I took off my Speck case which was given to me free by Apple. Sure enough, there are several scratches of various depth on the back of my phone which are visible in very normal, non-direct light.
My case was brand new when I put it on and I cleaned the back of my phone before putting it on. Stuff just gets in there. It's not a user installation issue.
that's horrible. let us know when your backplate shatters.