In ANH, the first scene is arguably all about Vader and setting up the larger conflict, even though we see Leia and follow the droids. Vader is the first named character seen. the other OT films are different but they're not introducing a world. Now TPM on the other hand begins with a sequence focusing on showing what the heroes are capable of, although the TF are shown to be the bad guys during. Many modern movies begin with a villain scene, (superhero movies especially, like the Dark Knight Rises or Avengers), but with new heroes, should the opening focus on them?