I do find this weird, you'd think Bioware would be trying to cover their asses and remove stickied posts on their official forums where they explicitly lie to the Mass Effect players. The only reason I could think of that Bioware claims you can get the "best" ending is if with the future DLC provides enough new Military Assets with purchase and completion so a player that doesn't want to or can't play multiplayer would be able to get over 4000 EMS.
Truthfully though,I don't know why Bioware went about this the way they did. I find it offensive how Bioware is literally punishing players that hate Co-op Multiplayer, don't have Xbox Live Gold, or don't have a broadband internet connection so severely. I mean they cut your war assets in half for not playing a separate and completely optional (plus possibly under-developed) game mode, something I've never seen done. It would make so much more sense to just give people that play Multiplayer extra Military Assets (for successfully completing a whole mission), that Bioware could cap off at a certain level.
Personally I've had a lot of fun playing Multiplayer when I was with a good group of people, however it is already getting old. If Bioware wants to successfully create a long term Mutliplayer fan base, they have to release DLC to change things up. One thing is that unless you die, depending on the difficulty you chose and your play style, the missions will last from 20-40 minutes. I would love to see shorter versions, like only 5 waves of varying objectives, or missions only of certain objectives. This way, it could cut down the time, and if someone doesn't like one set of objectives and loves another, they could get to play what they like instead of having to play each type in every mission. One other thing that I think that could be really interesting is if future DLC added actual story based/linked Co-op Multiplayer missions, possibly on Earth or the other home planets that are under attack. Plus I wouldn't mind having them add to the level cap, possibly giving more unique stat buffs (gold is still incredibly hard with high level characters) and more abilities with the chance to choose which 3 you want to want to use in the pre-game screens. There are multiple characters that have some cool abilities with some really crap ones, I'd love to have more RPG choices with my many characters. Also, one more thing, I wish that even when you promoted a class of characters, you could select like a max of 4or5 total characters to keep leveled up for when you play Gold missions, it could be your an All-Star team.