The problem with the whole "it should have been included in the game" argument with regards to multiplayer maps (and other content made after the game's release) is that, if developers did included the extra maps with game, then you'd have lots of people complaining about the game's release being delayed for a couple of months while the developers make the extra multiplayer maps.
People who by the game for single player would resent the game being delayed just so that the developers can include some extra multiplayer maps that they'll never use.
It seems to me that gamers want to have their cake and eat it. They complain when the release of a game is delayed for what ever reason, but they also expect additional content to be included in the initial release... like they think the developers have some sort of magical time machine with which they can release a game, view how the online maps are being played and received, make additional maps to cater to the trends they're seeing, then go back in time with these new maps and release them with the game.
It's they same when people say that issues only discovered after the game's release and hundreds of thousands of people start playing it online, should have been patched before it was released.
How? No matter how great you think you're favourite developer is, they're not omniscient.
I'm also aware of the other side of this argument, the whole 'nickel and dime' trick that some publishers do when the content is actually on the disc, but locked.
Publishers who, at a later date, charge extra for 88kb files are shits, and part of reason why some people seem to be so un-accepting of DLC and obtuse in their understanding of the development process.