I've played in games where the status quo is not changed, and have always found them to be okay, but when a GM opts to change the status quo, to sort of turn the setting on its head and shake it a bit, it tends to be alot more interesting.
Players can't take things for granted the same way. It makes them second guess things and makes the whole world a lot more shades of grey then black and white.
It has also, for me as a GM, totally eliminated the book nerd response from players of "But page 163 of blahblahblah sourcebook says the NPC is like this..."
And that alone, makes the work of integrating new official material into my campaign totally worthwhile. The changes to cannon that I have made have also assured that I know my setting better then I would, if I were just using a canned setting. I have to integrate new material if I want to use it in my game, and that means that I have to think about where everything fits in.