I heard they changed a lot in the two towers, but I think it is cool that they show Gandalf in the trailer- going on the assumption that everyone knows the story already, and ignoring those people who don't know it, saw the first movie, and will probably be shocked when gandalf re-appears in The Two Towers.
GANDALF GOES FUCKING NUTS
Wizard slays 16 with sword disguised as British flagpole, maimes 72 with 'Hat of Doom'. "SUCK IT, YOU LIMEY PRICKS," shouts saucy magician.