One small twist between the plots of the book and movie versions makes it inappropriate in the movie.
In the book, the Ring corrupts Saruman – like many another, his lust for power overcomes his wisdom, and he “commits treason against the Valar” to set himself up as supreme, in place of Sauron.
In the movie (like the books, the movie sequence should be seen as a single tripartite whole), Sauron corrupts Saruman, enticing him over to the Dark Side, so to speak. Hence the fall of Orthanc is not the destruction of a separate menace (except that of course it proves not to be) but a foreshadowing of the fall of Barad-Dur.
Then, too, the important characterization detail of the growth in responsibility of Merry and Pippin is omitted from the movie, allowing them to function (which was a true-to-book role as well) as foils for the tragic Frodo and the assorted High and Mighty Figures with whom they come in contact. Hence their coming into their own in the Scouring was never foreshadowed.
PJ took liberties with the story as told in the book. But as anyone who’s reviewed Christopher Tolkien’s edited versions of his father’s unpublished work realizes, Middle-Earth was a work in progress throughout Tolkien’s life. Jackson did not produce a travesty, but a variant retelling of the story, with details omitted and altered. With Tolkien’s taste for medieval literature, where the retelling by different authors of Arthurian, Rolandian, Alexandrian and other legend cycles was a commonplace, one can only presume he was smiling down on a fairly true-to-book adaptation for the large screen. (His comments on the abortive Forrest J. Ackerman adaptation in the Letters are instructive on his views about what a LOTR movie ought to be.)