Yeah, Lucien is right. In the movie they had to make some kind of antagonist towards Frodo and Sam. In the book, the Antagonist was Shelob, but that wasn't in the 2nd film. JP had to change it around. He made Faramir into a Antagonist. Though, it didn't change nothing. Sooner, or later Faramir would have done what he did in the movie.
The Scourging was a fun bit of post-storyline in the novels. It fit in with the books' dynamic, I felt. But I completely understand why it was omitted from the films. It wasn't terribly necessary (though not as little as Bombadil) and would have really weighed the last movie down.
And Frodo spending time in Ithilien would have been pointless in the movies. All these little editions and sub-plots, while charming in the novels, are just too much for too little in return. Again, would have weighed the movies down with hours of extra, boring scenes.