It sure would be cool if Microsoft communicated effectively about their games from the get-go.
Why would Microsoft even assume in advance that their flagship FPS title that has always had MP would be accused of not shipping with the aforementioned game mode? People are coming out of the woodwork with tales from their asses and they've done the only thing they could do which is refute dumb rumors.
Imagine falsely accusing say Ratchet and Clank of having an online only campaign despite that have never being said and getting annoyed at Sony for not clarifying that in advance.