the other day, i was browsing the articles at gamedev.net when i came across an old ebook titled "the secret are of computer adventures". even though a lot of the stuff in it is outdated, it's still an interesting read and, imo, has a gold mine of information in it.
linky (http://www.gamedev.net/reference/articles/article246.asp)
"Although they are largely an intellectual medium, some adventures are accompanied by a little tune that plays throughout the game."
Hahaha, I love it.
Thanks for the link - it's very interesting.