The "nothing" that Wrath did was much more than the "nothing" accomplished in the Cata or Mists trailer. It felt more personal, contrasting the once noble future of Arthas and his potential to be king with the monster that he had become. All in all though, it really just gave you an idea of the type of villain you were up against.
But in general, cinematics do evolve over time in their focus.
Classic: Horde-Alliance combat, your character, the classes and races. (tiny bit of lore, "four years have past" etc.)
BC: Classes/races(BE/Draenei mostly), horde-alliance combat(less), Villain & lore
Wrath: Villain & lore
Cataclysm: Villain (No lore, even though Deathwing had pleanty that they could have used)
Mists: Horde/Allaince combat, mixed messages towards the Pandaren
Take from that what you may. Interesting to think about how cinematics might work in the future.