I recently downloaded with minecraft launcher the new music but as I tried to listen the "boss.ogg" file with VLC player I noticed that it sounded as there was no music. So I opened it with Audacity editor and I saw that there was a music - but it was too quiet to be heard at all. Normalization with a sound editor fixes the problem.
So there is the boss music (and can be heard after editing it), but I don't think it's supposed to be that quiet.
Edited summary to clear the ambiguity.
I disagree with the "Works as Intended" resolution to the bug - the boss music for The End is really too quiet, even in comparison to the other Minecraft tracks. Unless it was intended to be a silent fight, then it shouldn't be classified as "working as it should".
Please note that I only reported one track as a problem, not all. It's Talven81's later editing that changed the summary to a more general one.
I was fighting the ender dragon yesterday. I was really disappointed that I didn't hear any music during the long fight.
Edited summary to clear the ambiguity.