When I was talking about compression I was not talking about the videos. I was talking about textures and things that are normally compressed to save space. I highly doubt voice work is the cause of 3 discs. Look at GTA: San Andreas. How many hours of voice work/music was in the game? I rest my case on the music/voice aspect of it

EDIT: Unless they are using uncompressed 7.1 surround sound...then maybe.