I can confirm that the ancient music does play in-game, so the theory that they're named incorrectly doesn't hold water. There are times, however, when nothing seems to be playing. I'm guessing it's just a design decision to not play music end to end, perhaps for fear of it getting repetitive.
TheBarnacle is right that the music fades out when you zoom very far in. It gets replaced by sound effects (ex. birds if you're over forests). Also, if you're zoomed in and over one of your cities, you'll hear lively music that is different from the game's general ambient music. If you don't hear anything when you move over your city zoomed in all the way, then you have a bigger problem.