According To Him “6 gigs: New engine & we’re much better at compression (art/voice/data). It’s huge yet more optimized than we’ve had before. And faster.”
So there you go, you Skyrim fans can now rest and know that nothing has been sacrificed to fit the game on one disc.
Also, I find the capitalized "Him" somewhat amusing.
Edit: Actually, the entire "article" comes across as sarcastic, no?