Really effective literature takes you so deeply into the story that you don’t know or care that it’s fiction.
We, as readers, are partly forced to view the author’s world through the lens he used: sometimes as close as inside the protagonist’s head–knowing no more (and often quite a bit less than that protag). Older novels were written much like histories–James Michner‘s tomes spring to mind. His Hawaii and Alaska started with plate tectonics and Centennial with dinosaurs.
It helps, of course, if we understand and agree with the author’s world view, but sometimes the fun lies in an “unreliable narrator” who intentionally or not lies–perhaps to both himself and to the reader.
For avid readers of a genre, author or period, this immersion becomes problematic when the reader thinks she know more than the author, or feels that subsequent authors have betrayed the history, economics, religion, world force or what-have-you of the fictional world.
Which brings us back to Star Wars. In addition to the issues so ably discussed by Gladstone, the Star Wars galaxy is in danger of fracturing into several parallel universes. The “canon” laid down in the six (or three, depending on who you talk to) morphs into the “extended Star Wars universe” chronicled and dozens of books by a variety of authors. The Clone Wars TV series overwrites some of the extended universe with a different story. And the coming SW episodes VII, VIII and IX promise further muddy the water. (Not to mention Disney Inc.‘s demonstrated tendency to merchandise the daylights out of whatever they produce. Such as: we can count on there being a princess in the new series.)
My opinion? It’s all for the better. “Let a hundred flowers bloom; let a hundred schools of thought contend.”