I can only surmise that the producer thought death by car bomb was equal justice considering thats how Fabrizzio killed Apollonia. (I believe that death by Fabrizzio's own lupara was a more "personal" touch).

Back when I was in college, and the movie came out, and movie posters were hung throughout the college dorms, one of the most popular was of Michael Corleone wearing his white hat and holding the shotgun. It always surprised me that the scene was never in the movie.