Yes, DRM has been cracked in the past, but it gets harder and harder each cycle. Even Blu-Ray hasn't been fully cracked yet (it is still a race with each individual movie.)
That "race" is as effective as having a full crack already. Why work harder? I'm not sure anyone is really working on an effort to fully crack bluray anymore. Cinavia on the other hand people are actively working on and there are a few workaround already, but this is an end device problem.
The biggest problem that separates bluray from any kind of audio is the fidelity problem. The analogue hole was closed by switching to all digital links, and we all know the expected quality of pointing a video camera at the TV screen. On the other hand producing sound is an inherently analogue process, and high quality recorders are actually cheap. You can't close the analogue hole without removing speakers from the equation, and any signal that is sent to speakers or headphones can be recorded with very low distortion on relatively cheap gear.
So while typical cinema camera jobs make people's eyes bleed, I don't think 99.9% of people would notice if you re-recorded a signal, resaved it and served it up on the internet. Well some people notice, like those people who ripped the Metalica playlist from Guitar Hero and served it up on the internet. People noticed because it actually sounded a shitload BETTER than the album ever did.