MMO crunch asks is borderlands a mmog, and in doing so asks if there is a story http://www.mmocrunch.com/2009/11/09/is-borderlands-a-mmog/
This is what I had to say in short:
In terms of story, I always look at gamers who expect to read a story in an interactive medium and think “Wha!?”. It’s an interactive medium – YOU make the story.
What I would grant is that these games, not at all right now, have any tools to record player actions and layout a story (or atleast a log of cool events). So it’s easy to forget the story you just made.
I wrote more on my other blog