Not just you. There is a slight Curve to the back from side to side. Not sure why, but from a design perspective, this curve will allow the device to lay flat on a surface with less rocking that a perfectly flat device would. Unless both surfaces are perfectly flat, the Device would rock. Making the Surface slightly concave would improve it's ability to lay flat without rocking. Ideally three points of contact are the best, but that would look odd on a rectangular device. Again the design comments are just my speculation as a design engineer. Wonder if they would look at me weird if I stop into the Microsoft store with a straight edge and start checking the display units. I bet the sales associated don't realize the back isn't perfectly flat.