What are the chances of a comment from the board designer?
Zero point zero zero.
My guess is the thinking is that the diode where they put it does not limit the current into the Arduino normally and does not drop any voltage either. The "protection" comes from the power supply you plug into it going into current limit. Also it is not that easy to blow a 1A diode, with a 1A load it will take some time over heating. Anyway that is my guess, I am not saying I agree with it.