At the rate they make these phones and the unforgiving nature of the buyers (many of them), **** happens.
If Apple said they needed a week to hand stroke all phones to make sure there are no visible flaws then do you think that would go over well? You're talking to a group of psychos who have literally sat around all week tracking a box in a warehouse, on a plane, on a truck to their porch.
Flaws will happen, Apple will cover it most likely unless you're being completely inane. I think the pic posted shows a cosmetic flaw that I would deal with until the overall hype settled down. I'd then make my way to Apple and get myself a replacement. No worries.
Recommended reading:
Quality Control for dummies