The problem is polygons. Bethesda needs to use this technology for TES 6:
http://www.youtube.com/watch?v=00gAbgBu8R4&feature=socblog_ti
That technology is completely unproven (to be useful for gaming) and as of now is all theoretical, in-the-works stuff of which I'm personally skeptical. I've no doubt that it exists, but can it actually be used for games? When I can see a proper tech demo incorporating animations and an actually interactive portion of gameworld, I may believe it, but as for now, it's simply not viable... and can you imagine how much HDD/SSD space such a thing would require? Polygons are the best-proven method available for game development and I don't expect that to change any time soon.