Earth being the target and humanity being the primary victim is an easy thing to write. JJ Abram's Star Trek, for all it's attempts to say that things will be different in this universe, still conformed to Earth being in danger and that planet needing to be saved above all else, just like it did four out of the nine movies previously.
I think when you boil it down, Bioware's treatment (Whether encouraged by EA or not) of Mass Effect 3 shows that their number one priority is to appeal to the more casual gamer that has never played a single Mass Effect game rather than taking the steps to ensure that everything that goes on in ME3 feels like it belongs with the previous games. And like a lot of movies, games, and TV shows that just want to appeal to the ignorant masses, it doesn't offer any cadence or pace to set up what's at stake, but instead resorts to throwing you into the action offering only moments of pathos like that kid in the opening. Even Earth, the planet that every trailer, tagline and article talks about saving doesn't really seem that important. For instance, how many aliens did you see on Earth? Compare that with how many aliens there are on the Citadel, Omega, Noveria, Illium, and even Tuchanka. All of those worlds have different species of aliens that are not indigenous their, and for the final installment of this galaxy scale game, we'our goal is to save a planet THAT DOESN'T HAVE ANY ALIEN DIVERSITY in it's population. While I'm sure we'll get to visit other worlds and potentially save them from the Reapers, so far everything Shepard does int he game is about "Earth's Survival" (Rescuing the Krogan female). That's a big disappointment.
