From the actual movie...Gandalf is not wearing his Ring of Power on the Bridge at Khazad Dum and there were 2, maybe 3 "elk bugles" (most of the BR screams were those high-pitched ones.)
Did you see Merry's bloody forehead? The fact that they stuck to the book with that as well makes me so happy! Just a little thing, but means a lot to me. Now if they will just show the orc rubbing that dark substance into it...I'll be in heaven!
I think maybe they're using a visual to emphasize what Gandalf said at one point, that in some ways he IS Saruman the White--as Saruman the White should have been. I think making him look like him is part of that, plus he has to look different enough (and enough like Saruman) that our three highly intelligent, observant heroes would not recognize him without looking foolish.
I also think PJ is using comparison-contrast with Gandalf and Saruman--by making their appearance somewhat similar, you see how it is that they differ.
The only thing that I'm not sure about is the way Gandalf is speaking--I hope that we will still see the kind, personable part of his character. He seems a bit unapproachable in the preview, it'll be interesting to see how they hang on to some of Gandalf the Gray's personality. Maybe it will be the hobbits in particular that bring that out in him...