A brief point of order: In the film, The Fellowship of the Ring includes the first chapter of The Two Towers (Boromir's fate). The Two Towers film actually ends some way short of where it ends in the novel (just after Shelob's lair when Frodo is captured by orcs, and once Pippin and Gandalf have ridden off towards Minis-Tirith). Still, I get what you are saying. There do seem to be natural dividing points for the films.