Another thing to note is the game is running on the same engine as previous games and Bioware have stated that they have optimised it for the game quite early in the development process. After all, this is a sequel of a sequel, it would stand to reason that it would less "resources" to make. Consider those extra "resources" the ones they are using for multi-player. I will probably give multi-player a wide berth myself, as some other have noted Mass Effect games don't scream out to me "MULTI-PLAYER", but I'm not too fussed about it's inclusion. As long as my single-player is intact I'm happy, and nothing says to me otherwise.
It's simply factual those teams working on the multiplayer could be working on other things. Free DLC is the best example, multiplayer is totally different than say, adding in skins, it's a feat that requires a large team. I don't think that parts of the single player were directly cut, but indirectly. Time is still limited whether you have 1 team or a thousand. There is always something better than multiplayer to do (for me, again).
Co-op is not a campaign based mode. It is match based player vs waves combat where you play a custom created generic character. Matches will consist of killing progressively stronger waves of enemies, along with some objective games like disarm x amount of bombs while things try to kill you.
---------- Post added 2012-01-31 at 02:44 AM ----------
Free DLC is something Bioware actually does from time to time. Basically, once a game is 3 months away from being done, you can't put anything else into it because at that point you start production of the physical discs. Those last 3 months are used to do stuff like test and patch the game, as well as make new content. Because of the advent of DLC companies can design new content for the game without being restricted by the physical discs, thus first day free DLC. That is how we got Zaeed and the Normandy Crash site in ME2. They were day 1 free DLC.
so sad Krogan Vanguard will not be available...
Dont care at all for the multi-player in mass effect