Hitchcock sensibly made his ending more visual and more dramatic, but what gives the novel extra interest is its Second World War setting. The first part of the novel takes place during the so-called "Phony War" period of 1940, when the French (and British) populations were confident that the war was going to end with a whimper, if it ever managed to get going. The final section of the story is set in late 1944, with France mostly liberated but still demoralized and licking its wounds. Madeleine's deception is meant to find its echo in the Phony War, and the revelation of her role in the plot is, I think, a symbolic reference to those French who collaborated with the Nazis.
Boileau and Narcejac (they were a writing team) had a reason for setting their story during the war, and this added political component gives the novel more depth, more resonance than the film version. Usually writing teams are a recipe for bland prose, but this duo's writing is lively and clever, even stylish. If Vertigo the film is about obsessive love, Vertigo the novel more about betrayal of both the romantic and political variety.