As you know, there are a few tricks and you can "fly" or travel beyond borders of Skyrim and see the land from Cyrodill and Morrowind. Of course, it is all created with low res textures and not finished at all, but why do you think that those parts are appearing and rendered in the game? What's the point?
You can see it for example in this video (for those that doesn't know about what I'm talking about) -> http://www.youtube.com/watch?v=JChFFdNoCrI
Is that maybe because the want to have that part of the map in the whole skyrim engine for some reason? Some dlc related thing mabe?
Just guessing (and hoping).