It's probobly the same thing as why when I wear my glasses I don't notice the curve in them, but friends of mine talk about the "Weird curves" in their flat sunglasses. Different people, different perspectives. Also, could just be how your eyes focus. you could have perfect vision and still have problems with monitors, while I need glasses and can stare at a screen all day without eye strain. Everyone's eye's just focus a little differently.
Shrug