Did anyone else noticed this?
Truth be told, they are the same. Thing is, the PS2 is somewhat limited in power, so they compressed the graphics and music/sound immensely (made obvious by their tinny voices). What you’re hearing in-game is essentially the same music, just much lower quality with some of the more exuberant parts of the music pieces cut out.
You can find the .psf files here:
http://tzone.org/~llin/psf/
Search for Final Fantasy XII. Right click on RAR and ‘save as’.
To play these files, google and download Winamp.
Then download this file:
http://www.neillcorlett.com/downloads/HE209.zip and install.
EDIT:
By the way, I would say the songs on the OST are actually the way they were supposed to be in the first place. Technical limitations forced them to downsample the music and voice acting in the game quite a bit, like Puyo said. OST sound quality > game sound quality.
(scroll down to find it.)
[FLAC Lossless] Final Fantasy [ALL] [MegaUpload] (Thread 39118)