Jim, sometimes your brilliant, and sometimes you manage to start out with a premise so inherantly flawed that it ruins anything you might have to say later. In this case the idea that the outcry over the "Mass Effect 3" ending shows that video games have somehow "arrived" due to the outcry... yet really we've seen all this before with say "Final Fantasy VII". FFVII having been what probably actually showed video games becoming a big deal a long time ago, and doing it much the same way by having an absolutly Sh@t ending. An ending I might mention which lived on in video game infamy for a very long time, until the game eventually received the finale it arguably deserved as a full length animated movie called "Advent Children" which didn't satisfy everyone bit was pretty well received by the fan base.
Like a lot of people who defend the industry and writers, you seem to head into the entire "well, they couldn't make everyone happy" defense, the implication that the problem is with the fans rather than the writers, as the fans would have been upset no matter what is done. That's not really the case however. In general a decent ending that doesn't match the preceptions of fans will generally be accepted, with various people saying "that was okay, but I would have done things differantly" and leaving it at that. The kind of hate you see here comes from an ending that is utter crap and manages to piss off the vast majority of people who experience it.
Pointing a finger at Star Wars is kind of a good example on a few levels. For one "Mass Effect" was stated to be the spiritual successor to a Star Wars game called "Knights Of The Old Republic". For another it shows how a proper, well written, ending can redeem a lot of flaws. The sheer awesome inherant in the final battle in Star Wars which tied up the loose ends and saw the redemption of Darth Vader, caused people to receive the movie well despite mocked elements like say... the Ewoks. By the same token a crap ending really CAN destroy entire series by turning them into downers or leaving the watcher unfulfilled. Who the heck wants to watch 120 hours worth of something only to find out it's all futile, the bad guy wins, and everyone dies horrible, pointless deaths? Endings which aren't endings are the worst of all.
Let me make an analogy I've used before.
Let's say your watching the original Star Wars trilogy and everything is like you'd expect up until the finale. Just as Luke is entering the emperor's chamber the screen whites out. Rather than the end of the story with the redemption of Vader and the destruction of the Death Star, and freedom in the bloody galaxy, we're treated to a 70s esque light swirl of the type usually intended to simulate an acid trip. In the middle of the swirl a rainbow hued cartoon platypus appeals and introduces itself as "Mingo" the embodiment of the force. Mingo proceeds to ramble on about the events of the series so far, the natures of the light and dark side of the force, and what might happen here... but being careful to say that what seems to happen might not actually happen, much like Luke's experiences in the cave on Dagobah... oh and maybe he never left the cave. Then the end credits roll... assuming you manage to sit through them (or are paralyzed in shock) you are treated to a scene of some old astronaut with a hippie name like moonbeam and borderline alzheimers on a nature walk with his grandson, who is begging him for another tale of "The Skywalker".
The thing here Jim is that if George Lucas had ended RoJ that way, there would have been no massive continuation of the franchise in anyone's hands, and he never would have had the oomph to get prequels made so he could screw things up. After all who the heck would want to see a prequel to that?
You can't put crap writing on the fans, and an ending that manages to cheeze almost everyone off is always, always a bad thing.
EA/Bioware ignoring people is not the right thing to do here, it's arrogant stupidity, especially if they want a franchise out of it. They are in a position to make things right, much like what happened when "Farscape" got cancelled on a craptastic cliffhanger and they did a mini-series to finish off the series (Peacekeeper Wars) and not have it end on that note. With all of the money EA/Bioware has made there is absolutly no reason why they can't come up with a proper ending, which will by no means be universally loved by every fanboy, but won't be reviled either. Hating the ME3 ending is one of the few things pretty much the entire ME fanbase can agree on (there are of course exceptions, like there are to everything).
I'll also say that unlike TV series like "Lost", "Mass Effect" costs the people playing it money and thus customer satisfaction is a big deal. If this was a movie, you would have had people storming the ticket booths demanding their money back (it has happened before) which would have been blown right back up the chain by theater owners to the production company. You'll notice EA/Bioware doesn't seem to be in a hurry to buy back all the copies of the Mass Effect trilogy they sold. If they were to say offer everyone $60 per game (up to $180 per person) for the software... since this reflects on the whole thing, you might have a point. Right now you can't viably get your ticket refunded and that in of itself puts this in a position differant from movies, or TV (which costs nothing). Part of the reason why there are campaigns that are so extreme to demand "taking back" the series, that investment not just of time but of money does affect how people think in cases like this.