Edit: I'll tun this double post into a response.
No worries Mantidor I am often over looked

Thinking back on it I may be wrong with the battle cues, it's been a while since I played TP. I think I made an error.
It may have been that the musical CHANGES that occur during the gameplay could not have been done with traditional orchestrated music and such midi style music was used.
Example: While riding through Hyrule field the over world theme plays. Now an enemy bird approaches behind you. The music begins to shift into a darker theme and an enemy theme begins to overlay the pre-existing track.
I think that was a primary reason for not having a full orchestrated track. Though also thinking back on that scenario I do remember hitting the birds and I could remember the music having added "beats" for the attacks done on the bird. Not as prevalent as in WW but I thought they were there. . .
I'll test this out as soon as I can free up the TV my Wii is connected to =).
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Update: Yeah I guess they aren't there. My mistake.
So I guess the "reasoning" behind lack of orchestrated music was for those musical shifts at certain points . . . I guess. I'll try to find a source on that.
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Update: Well I stand corrected. I was wrong as to the "why there is no orchestrated music in TP" so I apologize for my misgiving of information. In an interview with Koji Kondo on IGN we get the real answer:
Quote
IGN: Many fans were expecting the Legend of Zelda: Twilight Princess to support a fully-orchestrated score. When we talked with Aonuma just a few minutes ago he mentioned that the lack of orchestration was something that you were deeply let down by. Was it limited by a budget or time constraint, or was it something Nintendo wasn't interested in?
Kondo: As far as Twilight Princess goes, of course those decisions took place. In the end it was not about the time or budget; we had the time and the budget, and it wasn't a Nintendo philosophical stance that "we're not going to do this". Basically while we were working on the game and creating the music, we never really felt that this was a place that needed a full orchestra. We never got the feeling that "Oh this would be a place that could make more of an impact with a full orchestra". We just didn't see the need for it this time.
If you power the game up and let it sit there's a fully-orchestrated piece there, so we aren't against doing it, no.
There you have it. Real shame. Maybe in the next game there will be a full orchestrated sound track.