I teach (amongst other things) a course in fantasy literature at a university  in Canada and one of the most interesting aspects of it (for me) is how fantasy and imagination gets channeled into all kinds of new forms (especially in the last 30 years or so). Yes, we'll be reading classic short stories and novels, but we'll also be discussing a graphic novel, a computer RPG (Planescape: Torment) and D&D.  I even toyed with the idea of assigning "Tomb of Horrors" (but decided there was too much else they'd need to know to get into a discussion of it).  All this may sound a little weird (as not being very "literary"), but I figured that the point of fantasy is to push boundaries, so why not?

Really, my secret agenda is to brainwash all my students to pick up and play 1st edition (although I'd be happy even if they started in on 4th . . . ).

So sure D&D is literature -- why not?

I believe that (A)D&D actually helped me gain better grades BITD, as it opened a new world of fantasy literature which in turn gave a direction for my own writing and increased my vocabulary.

Whilst neither being a blunt stick nor the sharpest tack in school, it certainly gave me confidence to discuss points with a better grasp of the language.

It also helped develop an imagination that certainly seems to be evident in my kids too!  

I don't think the idea (overall) of D&D as a beneficial teaching tool should be neglected. While I would never condone it as a part of a curriculum, the benefits of the hobby for young minds is certainly there.
Reading and understanding a rule book takes, or illicits, thought. Kids have to be able to read and comprehend. While many already possess the skill, those who are weak will improve their skills. This goes well beyond D&D and includes any game system, be it a rpg or a strategy board game.
Simple math skills are constantly used. Some games more than others. Champions, for example, requires plenty of math to generate a character. And playing the game requires constant simple addition and subtraction - again, the kids may not be learning anything new, but they are basically doing loads of homework without knowing it. Repitition is a good thing.
I know I dodged the "literary" aspect of the original post. And to be honest, I do not consider D&D or any other game a work of actual literature, though I would agree that there are elements here and there and some are very, very good.