Dual layer DVDs can store just over 8GB, IIRC. Compression (of game data) might've improved as well, though.
Thanks for the information. Particularly interesting as I recently heard that Killzone 3 [an FPS for PS3] comes in at just under 40Gb. I'd expect Skyrim to be bigger than that, to be honest.
I suppose it was that size, it'd rule out downloading entirely until broadband speeds had improved dramatically.