I was wondering how it was that METROID PRIME still managed to get a soundtrack album produced in Japan when the game in question did poorly there.

Scitron used to be good for publishing a LOT of stuff, even soundtracks to games that didn't sell super well.  Since their disappearance we've seen a lot fewer things like Nintendo OSTs. 

One of the reasons why I was asking was because I was trying to entertain the idea of Nintendo actually releasing a soundtrack of some sorts to its newest Zelda game, Skyward Sword, which, IMO, has awesome music.  But the last full soundtrack of a Zelda game we ever saw was "The Wind Waker".  Since Nintendo made CDs of Super Mario Galaxy 1 & 2 for its Club Nintendo members, even though neither were particularly huge hits in Japan, I wondered if it would do the same for this one, since it too has an orchestrated soundtrack.

Does sales reception have anything to do with soundtrack releases or not?  Case in point:  Muramasa and Opona were not huge sellers in Japan (the latter, in particular, was a commercial failure), but both still got OST releases months after their releases.  Likewise with Arc Rise Fantasia.  ON the other hand, titles like Little King's Story and Earth Seeker both of which flopped in Japan, didn't get any OST release.

Which is why I find all this rather confusing.

Weren't Super Mario Galaxy 1 & 2 sold fairly well in Japan? (above one million).

Case-by-case. A big hit of one game can imply there is not a small amount of fanbase that can become also potential buyers of its soundtrack, but it still might not motivate record companies like Sony or King Record enough to release game soundtracks, the average sales figure of which is less than 1k, while smaller or game-specific companies like Team Entertainment would.  Also, Muramasa and Opoona are actually self-published by Basiscape, and they are kind of indies (although Muramasa OST still sold 2,000 copies the first week), so I guess it would cost less to release soundtracks.

Mario Galaxy did all right, crawling slowly to 1 million, but its sequel didn't quite get there (even though it got off to a better sales start).

@ Cedille:

Is there a sales tracking site somewhere that has figures for videogame soundtracks and/or sales data from past releases that you know of?

I thought I'd throw this in here since we're talking about Mario Galaxy but the soundtrack is now part of a new Wii bundle in the ad I saw at work.

I saw the same thing when I was looking for the Dark Souls Limited Edition. I think it comes in a cardboard sleeve rather than a jewel case. That's the norm for American releases of a lot of soundtracks.

I wouldn't doubt that.

Oh I thought the sequel also reached into a million, but according to Nintendo themselves (they might have put the number of shipped copies).

I don't know a site that archives data on accumulated figures, but I mostly refer to a weekly/monthly report of Oricon (I guess a fee-paying member can read the past data). Game soundtracks usually sell pretty poorly, but sometimes occasionally ranks around the bottom.