But... Why is the wing of airplane shaped like that?

Gee, let's check that, shall we? A quick tippity-tap into the google machine and we find... "A solid body moving through a fluid produces an aerodynamic force. The component of this force perpendicular to the relative freestream velocity is called lift. The component parallel to the relative freestream velocity is called drag. An airfoil is a streamlined shape that is capable of generating significantly more lift than drag."

So if you asked Orville or Wilbur they might indeed give you answer about the faster on top part.

They might indeed say that, and they would indeed be wrong when they said it.