That second photo you linked, is the only other one I have been able to find, aside from your own, that has the white material showing. I am guessing there are more out there, but were you an early adopter? Could it be something Apple quickly changed?
If you have an Apple store nearby, maybe you could ask them their thoughts on it?
Thats the only other pic I could find too, but you need to have light shining in the hole to see it so maybe that's why.
Anyway, I just bought it maybe 2 weeks ago from MicroCenter as a new open box item. It's not an early version, it is the one with the black sport band, so it's not that old.
I have AppleCare + on it and it functions perfectly, so I'm not taking it in. If anything happens I'll bring it in then.