This doesn’t pass commen sense for me. Plywood measured in metric, converted to imperial if needed? I can imagine someone coming up with 4 feet by 8 feet as a standard size for building material. I don’t see them coming up with 1220mm x 2440mm and thinking “nailed it, perfect size for calculating how many of these to make a wall!”

Also, since the gap between plywood takes space, plywood (and drywall) is a bit less than stated size to give you breathing room to put 4x8s repeating every 4 and 8 feet.

That said I don’t know why a nominal 2×4 is actually 1½ × 3½. Used to be finishing work shaved it down, now they just make ‘em that way to be ornery.