You might have misunderstood the word "score". I meant the word as part of "film score" or "game score" in this situation, which might not have been the right word here.
And in that context the music to GT4 is not a big score. Don't get me wrong, the music works perfectly with the game and I think whoever made it did a great job, but if you look at what kinds of scores get released as sheet music...Star Wars, Lion King, Lord of the Rings, Amelie, etc. I'm afraid both the popularity and the musical depth of the music to GT4 is below that of forementioned scores.
And besides that: if a movie or game is popular it doesn't mean the music to it is or will be popular.