The Fallout games generally begin with one setup for the plot that then leads to something bigger (Elder Scrolls as well.)
You're usually given something (relatively) immediate, and then as you follow the Main Quest events get bigger and more dramatic. (For example in Fallout 1 you start with the relatively straight-forward task of finding a water chip, which leads to you discovering the Super Mutant threat, which leads to you being elected to sort of single-handedly deal with the Master. Or in Fallout 3 you begin with just trying to track down your father and get some answers, which leads to you rediscovering the Enclave, which culminates in you getting the Purifier up and running.)
Besides, one thing that bugged me in Mass Effect (which I actually really absolutely had a blast with) was that it took this "AI will always go evil" thing for granted. Almost without exception every time you encountered an AI it was assumed that it was evil - no ambiguity about it. They never even really attempted to justify that stance or give a background as to why AIs will always destroy their creators, it was just apparently a foregone conclusion that everyone was supposed to accept.
Personally, I think it would be a tad more complicated than that. If we're going to take the stance that every time someone creates a self-aware program that it's going to turn on us and try to destroy everything, then at some point in the story I'd think you'd want to explain why that would be.
So I'm hoping that things are a bit more ambiguous in Fallout 4. We've guessed for quite some time that the next Fallout would deal with Synthetics on some level, so that's hardly surprising that it'd play a role in the story. I just hope they take a less cliched approach than Mass Effect did with the subject matter.