I partly disagree with this. Yes, it is common that Fantasy/Sci Fi authors do tend to do thisthey are describing new worlds to the reader so this is inevitable. But I think that they are many authors who do what you describe as information dumping extremely well and, if properly applied, these sections can add a lot of depth and colour to the world and story. Personally I dislike appendicesI dont really want to go thumbing backwards and forth through a book so I can get a clearer picture. Anne McCaffrey does this a lot and although I have a lot of respect for the characters and worlds she has created I dont want to feel like Ive got an encyclopedia tacked onto the end of a story. I think this is best left to non-fiction, in general.

However, I think that many of the less well established SF/fantasy authors do tend to suffer from a lack of originality and certainly some strange innate desire to always write not just a book but a three parter. I review for SFX from time to time and I always end up with book 2 of an epic 3-part saga, of which I have not read the first (nor want to after reading the second.)