That year, 1990, was probably the strongest year in movies within the past 20 years. Any movie nominated for best picture could have conceivebly won. Dances With Wolves, though, stood out for its originality, whereas Goodfellas and Godfather Part III pretty much cancelled each other out due to the type of movie. If you don't believe that reasoning, check out Oscar winner history. It happens all the time.

*other notes from that years oscars:
Talia Shire and Diane Keaton were both submitted for Best Actress, neither nominated. Cancelled each other out? possibly. but an argument could be made that both could have been better in Supporting Actress Category. NoOne was beating Kathy Bates that year, nor should they. she was awesome in misery, plain and simple.

Bridget Fonda was submitted for Supporting Actress and Franc D'Ambrosio for S. Actor. Neither had a strong chance. interesting at the time that the producers of Dick Tracy sent out many submissions for the supporting categories including Madonna, of course Al Pacino, and Dustin Hoffman in hopes of getting as many nominations in acting categories possible. that backfired and they only got One nom and one major win for Madonna.

Pacino SHOULD have WON let alone be NOMINATED!!! But it was one of those rare times where everyone assumes he is a lock, so no one bothers voting for him.