I think it's more in line with the oft-repeated notion that the scar which he got at University was small, but his face was grotesquely burned and scarred the first time he put the Doom mask, still red hot from the forge, on, so it's even more of a self-inflicted injury.
I agree though, we should never see his face, ever. The horror is infinitely amplified with a "Less is more" approach.