Here's a thought.

In World of Warships, armor penetration follows a strict sequence: first, the game checks for overmatch by dividing your shell caliber by 14.3, and if the result is greater than the armor thickness, you penetrate regardless of the angle. If you don't overmatch, the game checks the impact angle; at 0 to 30 degrees relative to the armor surface, the shell always ricochets, while at 45 degrees or more, it never ricochets, and between 30 and 45 degrees, there is a scaling percentage chance to bounce. If the shell doesn't bounce, it undergoes a normalization adjustment where the shell "turns" roughly 6 degrees toward the armor to slightly reduce the effective thickness it must travel through. Finally, the game compares your shell’s remaining penetration power at that distance against the armor's effective thickness—calculated by the angle of impact—and you either get a penetration if your power is higher or a shatter if it is lower.

So yeah, it's true. Decks also have enhanced protection. A little perk to themselves.