Yes I know. But perhaps in an MMO, a genre that typically has persistent content additions, makes it more feasible.
As long as the game isn't too short, the idea of replaying the story in a different way with other characters in an MMO could perhaps be more common? I often play through other classes in an MMO simply to experience the other classes. Rarely, do I continue playing them though, because the story in an MMO is typically exactly the same. If the story of the game was unique to the character class, as Bioware plans to do with SW:TOR, perhaps people could get more longevity out of their games, and designers won't be hesitant to include divergent gameplay for fear of players not experiencing content.