Bigeyez sent me a funny chart he found at Hellforge, which shows how much the stories of Bioware RPGs are similar to each other. Somebody posted that chart on the Mass Effect 2 forums, and got an angry response from a Bioware writer, defending the classic story structure.
Actually that discussion is far from new. In Joseph Campbell's book on comparative mythology, The Hero with a Thousand Faces, from 1949, already discussed the idea of the monomyth, the idea that numerous myths from disparate times and regions share fundamental structures and stages. Bioware games conform to that monomyth structure, as do fiction works from Lord of the Rings to Star Wars.
What I think is that requirements of RPG gameplay limit the freedom of writers. The monomyth structure works well in role-playing games. The structure of the hero's journey perfectly fits the RPG structure of character development. It is easy to transform fiction with the structure of the monomyth into a RPG. Which is why there are lots of games based on Lord of the Rings and Star Wars, but no games based on, lets say, Jane Austen novels. A story like Pride and Prejudice simply doesn't have the structure and the setting which would make a good RPG.
MMORPG storytelling suffers from the game having no end. That clashes with the basic narrative structure of stories, which normally have a beginning, a middle, and an end. Seen as a whole, MMORPGs have a short beginning, an infinite middle, and no end. Thus storytelling in MMORPGs usually works by not telling one story, but thousands. Each story is short, has a beginning (quest giver dialogue), middle (you go and kill ten foozles), and end (you return and get a reward). The inherent repetitiveness of that approach isn't very engaging. And often gameplay is more efficient if instead of doing these stories sequentially, you do them in parallel, accepting all quests at a quest hub at once, then doing all the tasks, and then returning to the quest hub getting all the rewards, which further dilutes the impact of the story. You easily do a dozen or more quests in a single play session, so none of the stories is memorable, and would be better described as "errands" than "quests".
The *real* story of a MMORPG, the one the player is interested in, is a personal one. It is the story of how his character developed, how he interacted with other players, how he overcame major challenges. Very few games offer the tools to chronicle this sort of life story: You get tools like the armory showing where your character is now, but not a history of how he got there, except for the dates in small print in the achievement list. Everquest 2 had some web-based tools, but for World of Warcraft you'd need to use a third party application like Path of a Hero to chronicle your virtual life story. And of course even automatic chronicles would only tell the predictable story how you leveled up, and would need room for manual additions to tell the stories of your encounters with other players.
Single-player RPGs have an end, thus they can have an overarching story of the player vanquishing a greater evil at the end of the story. Nevertheless that larger story is often subdivided into chapters, main quests, and sub-quests, so often you end up doing exactly the same as you do in a MMORPG: Talk with an NPC to get a quest, go and kill some mobs for the quest, return and get a reward. The dialogue with the NPC might have several options, but sooner or later you realize that most of the time these options boil down to "accept quest", "don't accept quest", and "get more information". That isn't really much different to WoW's quest dialogue window, where you can accept, cancel, or scroll down to read more. You don't even really have the option to play the unhelpful guy, because if the NPC asks you to save his farm for him, and you say "no", you simply miss out on the quest and the attached reward. Which is why in MMORPGs with a "good" and an "evil" side the evil guys end up being exactly as helpful and nice to NPCs as the good guys.
In summary, I would say that storytelling in RPGs can be improved, but mainly in terms of delivery and pacing. There is little hope that these games ever will be able to tell a wider range of stories, which are significantly different from the monomyth structure of the hero's journey. Pride and Prejudice Online isn't going to happen.