I think much of the reasoning for 'Birth of a Nation's' ranking is that it was groundbreaking, changing the way movies were made. D.W. Griffith's use of closeups and story and character development had just not been done up until that movie.

As for Shawshank, if you think about it it DOES have cliched characters (sympathetic main character wrongly imprisoned/corrupt warden/prison rapist/loveable old guy inmate/nice young guy inmate who wants to make something of himself on the outside & ends up dead because his testimony will vindicate Andy and ruin warden's cozy setup).

BUT it's one of my all time favorites, too and regardless of all of the above the story is told beautifully thanks in NO small part to Morgan Freeman's performance and the past tense narration of his character. It was he who held that film together even more than Tim Robbins, he deserved his 'Best Actor' nomination and were it not for Tom Hanks and 'Forrest Gump', both Freeman and the picture would've received Oscars that year.

I think many would agree now that Shawshank is actually the superior film. But 'Gump' was a monster box office hit (which ALSO brought tremendous hope and inspiration to millions), and there was no stopping it or Hanks.