well, it can be that AH3 cant be released on retail version more likely for not being profitable enough to be breakeven on the usa market, lets face it, fighting games are niche, specially if they arent made by capcom or namco on usa, and ah3 is more niche because the astheics and concept behind the game, add that ah3 is not popular enough even in japan(from what some people have told me, so take this with a grain of salt), the lack of sales on japan, not breaking the 30k units for what i know, this can lead to the marketing team on aksys or perhaps examu/asw (who knows) to think that the best way is to release the game as a downloadable game on usa in order to have utilities, but from what we konw this brings a lot of problems, in order to be a xbla game they would have to strip a lot of the content of the console port to bypass the size limit
and in order to be a game on demand it has to have first a retail version, that in the theorical scenario could be prohibitive from a bussines point of view, add the policies of microsoft over the downloadable game, and you have a nightmarish scenario to deal, plus aksys is a small company
just a little scenario that i thought that could be possible, not saying that it was that what happened or something :P