film vs book

superbhyll
I stumbled upon this film quite by accident and thought that it was brilliant if a little depressing, however having watched it i decided to read the book (obtained from amazon for a few pence) result---It is one of the best books that i have ever read but Oh so different to the film
SO WHY IS THE FILM SO DIFFERENT!
To begin with the whole context of the abuse has been turned around WHY?
The protagonists in the book are wealthy midddle class why were they made poor in the film --do only the unwashed masses commit threse crimes in real life?
also in the book the events take place during a particularly hot summer --the whole point of tom standing through the car roof before the crash was to cool off---in the film this becomes totally pointless.
the scene with carrol conveys absolutely nothing wheras in the book it is pivotal to the whole story.
When i watched the film the first time it took a while before i realised that the events were not taking place in the outer hebrides---in fact it is south devon.
To conclude i have to assume the film and book are two seperate entities both making a point but the film in no way whatsoever doing justice to the book and i do not believe making the same point.
I read the book at one sitting and know that i shall read it again the film on the other hand is far too depressing