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.

Operative keyword: "done well." Most of the time, it's done terribly, and it just detracts me from the story. And it isn't even relevant. Take, for instance, a scene written in limited third-person seen through farmer Joe's eyes. Would he actually give a fig about the current political climate? Would he suddenly break out into narrating some creation myth of a mysterious fairy land half a world away for no reason? The exposition is also often extremely prosaic, and as a reader, I frankly couldn't care less about it. Yes, I like appendices, because it's optional, whereas if the info-dumping appears in the narrative, I actually am forced to slog through it. Imparting information should be natural. At the very least, say, a local courtier talking to a foreign visitor to explain etiquette and such would be less agitating.

Another thing I hate, hate, hate with an unholy passion in omniscient third-person is this: things like "Little did she know, her action would set the calamity in motions..." in narrative. Guh. Why would any author feel the need to put things like this in, I would never understand. This kind of "foreshadowing" has all the subtlety of a two-by-four to the head or a chainsaw to the guts.

Speaking of lack of originality... Blurbs on back covers. Rhetorical questions like "Can the intrepid band of misfits save the world from the Generic Dark Lord#44534?" or "Will princess Ivorywen Crystalline Pink be able to overcome blahblahblah and find love?" I genuinely yearn to throttle whoever put them there. Of-bloody-course the misfits will save the world, nine point nine five times out of ten, and the annoying brat will find love. For once, I'd like to read a story where the answers to these irrating rhetorics are a bit, fat NO.