I'm not sure that moral choices alone lead to "extreme video game immersion" or anything close to it, but that seems to be the message what this article on Game Podunk is trying to convey. The Mass Effect, Star Wars: KotOR, and (recent) Fallout titles are all referenced:
Let me explain first of all by explaining how gaming protagonists have traditionally been presented. Typically over-the-top with chiselled features, an impossible to create haircut and a desire to banish all evil from the world, the gaming protagonist has always been a bit of a softie. You'd never catch them being evil, not in a million years, as whatever they do is striving towards the ultimate goal of defeating said evil and sending them packing into next Tuesday. Then along came moral choice, and the ability to change your protagonist from scripted softie hero-guy into mass-murdering genocidal villain extraordinaire.
I think the first time I ever experienced this approach was during Star Wars: Knights of the Old Republic 2, where I decided on my first playthrough I would be Mr Nice, choosing all the options to become the ultimate nicey-nice jedi master. Oh how naive I was - I was completely missing out on all the fun of being the villain! While I felt bad making bad decisions and having the other characters vilify me for it, my powers were too busy growing at an alarming rate for me to care. It was sheer bliss to be able to be the villain for a change, choosing options that made the game world a miserable place and people hate me for it, all the while as my character regressed from shiny smooth skin into looking like the Grim-Reaper's butler. Now I'm a nice person - I've never had any violent tendencies or desires to be evil. But give me the option in a videogame and it somehow seems so very appealing. I think this is because I've always been forced to be the hero and being a villain was such a nice change of style that it seemed like something fresh and new.
Back on topic, the choice of black/white decisions in moral games allows the plot to be much more focused. Imagine if you were totally ambivalent to every statement in the game, you'd essentially be making no impact and just be sitting on the fence with a pondering look on your face. Instead games force you to choose a bad or good decision and both usually have their perks, rewarding you for not being Mr. Indecisive and taking action, like the videogamer you should be.