If you want the soundtrack the DVD and Bluray of the film would have the final mix down of the audio including dialogue, sfx, and edits to the music. The CD would be your only access to the clean music tracks.
As far as technical aspects most video DVDs are encoded with Dolby Digital at 48khz @ 192kbs and it's a 5 channel compressed multichannel format. The thing about mastering video DVDs is that you always have to consider the max bit rate that the disks will accept for both multiple audio streams as well as the video. The audio pretty much has to be compressed to fit in different languages and multiple channels for playback along with the video. The compression used is very good, but it is a compressed format.
With Bluray the technical specs are much higher, but I'm not sure what the standard encoding for disks are. Theoretically there is a much larger "bit budget" allowing for less compression and better audio quality. A quick look at the Inception Bluray online says that the audio is:
English DTS-HD Master Audio 5.1 Surround
French Dolby Digital 5.1
Spanish Dolby Digital 5.1
Portuguese Dolby Digital 5.1
It's good example of how mastering a video DVD or Bluray in reality can require multiple audio tracks that can effect the actual use of the technically superior medium. I'm sure you could rip the soundtrack, but how are you going to deal with the 5.1 channels?
Edited by JadeEast - 2/27/12 at 12:09pm