This always comes up, and I often seem to be on the opposite side of the argument from many players. I’ve usually found that those who have worked on the implementation side of both tend to feel that they are the same thing, but that thsoe who haven’t see them as somehow categorically different.
So here’s my stab at explaining why I think both are really the same thing; in many ways, there are far larger differences between certain kinds of text muds than there are between graphical and text-based games.