...when DRM-protected material is encrypted using the AES cipher, which there are currently no efficiently computable cracks for?
when DRM-protected material is encrypted using the AES cipher
DRM solutions try to allow playback of the media, while not allowing to create a copy. To make playback possible with current hardware the media either has to decrypted at the local host or it has to be provided in decrypted form already. In the second case no decryption is needed while in the first case the decryption key must be known locally to the media player. Thus it is only a question of extracting this (usually obfuscated) key from the player while the actual strength of the encryption algorithm does not matter much.
As long as the DRM is only implemented in software the necessary keys can be extracted and thus can be used to decrypt the content and remove the DRM. To have effective DRM you would need to make any kind of reverse engineering the key impossible, i.e. implement it with fully tamper proof hardware. But the usability and other costs associated with such a hardware usually don't make this a practical option for distributing media.
Steffen has the technical answer regarding the protection itself, but there is one big problem that makes any DRM pretty much useless in practice: The analogue hole.
In order to play the music, you have to remove DRM - so iTunes or whatever app it is has to be able to decrypt it.
And at that point it's trivial to make a copy. A copy from Line-Out will suffer a loss of fidelity, but a copy made between application and audio driver is not going to lose much in the way of quality.