That looks like chemical exposure of some sort. Do your hands sweat alot? Since its around the edges of the USB and the grooves at the back where moisture can collect.
Wow. Can you get an even closer pic using macro? It looks like chips of the plastic are missing - that's what it looks like around the camera. Sorta harder to see that on the USB. Any exposure to stuff in your pockets? Sand? Chemicals? Do you chew on stuff? Wow.
Oh dear where was you n9 made china or Finland?
Seems to me there are lots of fake stuff out there, and that include USB/SIM covers. But, each N9 is delivered with a rubber protective case that fits like a glow, gives excellent grip, looks nice and really do protect the device. Why not use it?
At a closer look, it actually looks like you have not removed the protective plastic. I find it hard to believe someone can be that bozo, but unless your device is fake, that is the only explanation.