The whole reason Bilbo was chosen was to avoid the unlucky number 13, so cutting the number of dwarves would have mangled the story. Radagast could have been cut, I suppose, but I kind of liked him!
I don't remember them even mentioning this in the film, and they focus a lot more on his ability to be a burglar and stealthiness and the unnoticed nature of hobbits.
I know there's no way they were going to just cut out half the characters from the film, but the number of dwarves really does seem pointless and silly. And the book is rather silly, but the movie is much less so (as a nine hour epic, it probably should be a little more serious), and having so many characters just detracts from this.
That's the films biggest problem, on a whole - it tries to be epic and serious like LOTR, but also silly and kind of kiddy like the novel. It's an awkward mix at times.
