Since film soundtracks often have a 5.1 Surround Sound Mix, most songs will be slightly re-mixed to fit this format, which could include putting the vocals towards the center channel and the instruments in the surrounding four. I used to pop in my crow DVD solely to listen to Big Empty in "Surround" on my home theater.
So yes, it's a re-mixed version for the surround sound, sounds really cool too. A similar process was used for the CORE DVD-AUDIO disc that emulated 5.1 from the original masters.