The problem is if you compare a movie to a book then nine times out of ten you will be quite disappointed. Which is only natural because think of it this way, if you decide to read a book then it's because you either really enjoy the subject matter, or you really like the style the author writes in. So the fan base for a certain book is much smaller, is very keyed into the details of the book, and very much in tune with the way the book is written and the message the author is trying to convery. Plus it doesn't cost 75 million dollars to publish a book.
Now when it comes to movies it's totally different. Movies have to appeal to a much wider base of people from various age groups, genders, and basically a wide range of people including some that go to see the movie just because they had a free couple hours and the trailer lookied interesting. So naturally they have to add various things into the movie that are not in tune with the book they are based on. Doesn't make it a poor movie nor take away from it, it's just the way things have to be done to appeal to a broader spectrum of people. Movies like the hobbit don't follw the books 100% that's for sure, mainly due to the reasons I just touched on. IMO they are still enjoyable movies to watch, and are much better than sitting through some of the other mindless garbage starring no talent actors like Seth Rogan and people that pass for actors these days
It's a movie, not a documentary, enjoy it for what it is is my take on it.