This has been a pet peeve with me on newer games for a while now.
I've always been a completionist about CD games. Every game must have there manual or I pass on it. (unless its a really rare game and its really cheap) You don't know how many times I've walked into a used game store, looked through their PS2, Xbox, GC games, find one i've been looking for, open the case and see no manual and put it back.
In the future when I look for Used 360/PS3/Wii games more, I'm going to be opening games and see no manual and think... "Did this game have a manual??" and I can see passing up on a game then looking up online if it had a manual or not, go back to the store and find it gone. lol