Actually Michael Gambon is messing with you. If you do a little bit of research you will find that Alan Rickman has actually read the books. He has been asked in interviews and answered that he has read them, a more recent interview stated he did read them just before they were due to film each one, but he was taken over by the hype and actually started reading them as they came out. Michael Gambon is well known for teasing journalists, it just amuses me that you and the other fans of the series have fallen for his joke and taken it as gospel. People who claim to be fans of Snape and Alan Rickman try looking up his interviews on Google and you will find the truth. Read before you believe this one interview and make lame comments about how disappointed you are.
I can no longer watch the films since Michael Gambon joined the cast. I would think an actor of his reputation would be able to cope with the differences between the book and the film, and would recognize the need to research Dumbledore's character. I don't think these movies were a place for Mr. Gambon to impart his understanding of a head master, but rather that of the author J.K. Rowling.
Yeah, I like causing trouble. It’s the teddy boy in me. I used to be a teddy boy. Feeling slightly inferior and wanting to cause a bit of bother and get some action going on in the room rather than get bored stiff. Michael Gambon