"All of us, except him, are going."
Translation:Ieder van ons , behalve hij, gaat.
Not a native Dutch speaker, but I think it's for clarity. Even though "hem" is technically the object form of "hij," using it would be confusing b/c "hem" as an object could refer to any "de" word that is singular. But if you use "hij," you know you are talking about him.