I could be wrong, but i'm pretty sure Square Enix said that they didn't have to compress anything in the PS3 version of FFXIII, but they did for the 360 version. If they were able to not have to compress any of the cutscenes, or audio in that game with the Blu Ray disc then maybe BGS won't have to with Skyrim?
The FFXIII cutscenes for the PS3 are still compressed, just not as much as the cutscenes in the 360 version of the game (which also have a lower resolution). If the cutscenes truly were uncompressed the game would have been shipped on lots of blu-ray discs. Even the video in blu-ray movies are compressed (but the audio often isn't).
Anyway, the PS3 version of FFXIII supposingly have 10 hours of 1080p cutscenes. With 24 frames a second, without any compression that would be 1920 (X res) x 1080 (Y res) x 3 (byte depth = 24bit) x 24 (frames) x 60 (seconds) x 60 (minutes) x 10 (hours) = 5374GB. And a dual-layer blu-ray disc is 50GB, so 108 blu-ray discs would have been needed if the cutscenes were uncompressed. Instead it was compressed down to 32GB.