You get seriously pissed off in a nerdy way when they don't include things that were in the books when they make the movies, amirite?

Film is a different medium than literature, it has different requirements, different goals, and a different person in charge. Changes are inevitable.

Only if it's something important. Like if Dumbledore kept a pygmy dragon instead, then Rowling released the books where Fawkes's phoenix-ness was important, and everything got screwed up. But if it was something trivial, like Harry's hair colour , I wouldn't care. But if Harry were some muscle bound badass, it wouldn't make sense for him to be bullied.