Lexor: I could understand lack of some extras like movies, but why some of games have not even manuals??? I think every game shout have manual "how to play it", right?
example:
http://www.gog.com/en/gamecard/age_of_wonders_shadow_magic :(
Sometimes either the rightsholders to the manual(sometimes they can differ from the ones holding the actual game IP rights) don't want to or can't release it to GOG for some reason or they have lost it due to the passage of time.
And then you got some games just plopping a PDF or some such style manual on disk so for those games there's obv. no seperate manual cuz it's in the game folder after you install it or on the DVD/CD/etc if installing from a disc copy.