About work again + True Blood season 2

Having successfully once again conquered Google Calendar Application Programming Interface by fixing the problems we had with our Uni's student timetables uploads into the Google Calendar I am feeling quite good. But I am also very tired and brain-dead now so I am celebrating by watching all the episodes of the "True Blood" season 2 in one go. My brain-dead reactions can be shortly summarized as "Eric - YUM YUM YUM. Bill - boo. Jason Stackhouse and his storyline is boring. but at least his penis is left alone in this season which is a great improvement."

I have a big question, though. Why is "True Blood" TV series so different from the books? My mind boggles - I am not usually too worried by small (and even big) deviations between TV shows and books. But when there are so many changes that "True Blood" TV show is 25% of the book and 75% of some other stuff, I don't understand. What is the point of it? How does copyright work in this case? It is like fanfiction or like re-writing the books.