If you're on Facebook, you've likely seen "post the covers of albums that had an impact on you" thing that's been going around. There are several versions of it, but the one that I did directed you to post 10 albums, 1 each day for ten days, with the additional note that you not provide explanations.
4 of the 10 that I posted were either movie soundtracks, or ballets. I seriously considered even more movie soundtracks, film scores, original cast recordings, and ballets. Why I eventually decided not to was because it had been not simply the music, but also the story, film, and/or full production that impacted me. (I decided on this distinction after having posted my first cover, The Lion King film score.)
Why did I decide on this qualification? I guess it's kind of the same reason that I won't list plays among my favorite books, nor playwrights among my favorite authors; plays are written to be performed, not read. You lose a large part of the play - even that which is left up to the interpretation of the director, performers, designers, and in some cases musicians - if you only read it.
Likewise, the music of a film or musical is just one part of the art. The full experience involves both viewing and listening. Take, for example, a recent project of mine. I recently went through my closet and, finally, after much debating, got rid of all of my favorite videos. (I kept a list and am slowing buying the DVDs!) In so doing, I also jotted down the soundtracks of some these favorites, with the intent to buy or download them. I have recently added the soundtracks for Hook, The Raiders of the Lost Ark, and MuLan to my collection. I love these films. I love their music. Or, at least, I remembered the music in conjunction with the films being awesome.
And that's not to say that the music isn't as good as I remember, but I actually did feel like I was missing something listening to these soundtracks rather than watching the films. And maybe part of it is that you physically can't fit the entire score of 90+ minute movie onto a CD; maybe the parts that I remember loving in the film weren't included, or were truncated.
Or maybe it really is that you can't have the full experience when you remove one aspect of the art from the rest of it.