I think it's just a little flexible. I tried that with mine, and it turns out it's actually slightly _convex_, I can't get both ends of the card to touch the keyboard at the same time. It's really, really slight, though.
This sounds more like someone being anal retentive than someone who who has been diagnosed with Obsessive-compulsive Disorder.
For someone that has extreme diagnosed obsessive compulsive thoughts, these posts claiming "Apple OCD" make me cringe.
Your laptop is fine. Just use it.
I barely see a difference, are you sure its concave and its not the result of some other factor, including the ruler used is not straight.Maybe its just me, but does the keyboard on YOUR rMB look concave at all?