This is not a Joke. This is the first Rolex Deep Sea Sea Dweller. The reason it has a perfectly domed crystal is because a sphere is much stronger than a flat surface.
The famous architect, Buchmininster Fuller was the first person to really illustrate this principle in architecture with the Geodesic Dome. If I am recalling my design history correctly, this evidence came from the design of a chicken egg.
Try this experiment to better understand this principle. Place a chickens egg in between your hands. Make certain the top point of the egg is resting against one palm and the bottom base is facing your other palm. Now apply as much pressure as you can, and you will learn that you can't smash the egg because it is stronger than you.