Here's another idea, someone else thought of and I'm starting to believe...the chamfered edge is not anodized after all, but is painted. The slate back is definitely anodized, but they used a different finish on the diamond-cut bevel for a shinier effect. I have a tiny nick in the chamfer of my i5, and I examined it with a jeweler's loop. It really looks like paint to me, not anodization. Paint would certainly explain the incidence of blemishes we're seeing, being less rugged than anodizing (paint is a coating, anodizing is a surface modification). Some are reporting seeing paint chips after dinging their phone's edge, which is hard to believe unless it actually is paint.
I wish there was some way we could contact Apple and simply ask them (assuming we coould get someone who knew what they were talking about).