Game Manager - simply use static variables?

Hi! I was reading about game manager. It's purpose is to simplify access to variables which mostly represent current state of game, or selected character, weapon etc...

My question is: Can I just have class where I would have:

 public static bool isRunning
 public static bool isLoading
 public static Player currentCharacter
 public static Weapon currentWeapon

or do I need and why I need solution described here: https://unity3d.com/learn/tutorials/projects/2d-roguelike-tutorial/writing-game-manager