"Harry Potter and the Half-Blood Prince" Trailer

OK, saw the movie. I can't understand when a book is a thousand pages long, why when the write the screenplay they have to add scenes that aren't in the book? I'm referring to the Weasley house being set on fire by the death eaters. Why add scenes when leaving out important scenes like Dumbledore's funeral? Despite this and other head scratching moments, it was a good movie. But I think the first will always be my favorite and Richard Harris will always be the real Dumbledore.