What I think DRM is really all about is ownership. When you buy a music CD, are you buying the music, or a license to listen to the music? What does it mean to own the CD? Software has had the licensing model for ages - you don't buy software, you buy a license to use the software. That's because computer people understood much earlier that making a copy of software has virtually no cost. The cost is not zero, since information is always a physical thing, but it's so low that a business model based on production and distribution (that is, the medium) will fail. So the model has to be based on the content, which means the rights to the content have to be controlled - i.e. licensed. "On Demand" is the ultimate realization of this idea - you pay for permission to look at or listen to something and then it fades away forever (unless you pay again).
One consequence of this is that the idea of a music collection will vanish. No one wants to collect media licenses. If you don't own your CD's, then collecting them is completely pointless. The other consequence is that if buying music is truly a licensing agreement, then the RIAA is free to set the terms. They could theoretically say that when you buy a CD, you're only allowed to listen to it four times. Anything more than that is a violation of the license. Or that you can only listen on weekdays from 9 to 5. They're holding all the cards - all you can do is choose whether to pay or not.
As an aside, one American pioneer got it long ago: Consumerist commenter Troy F. says that he has a vintage Edison phonograph with the following message:
No license whatever is granted to anyone to use this patented Phonograph with any reproducer or recorder or blank or parts not manufactured by or for us nor with any other records than Edison records and original records made by recording upon Edison blanks, nor in any altered or changed condition, nor if this label or said name plate or serial number or trademark be removed or defaced or changed in whole or in part.That's right - Thomas Edison was saying you were not permitted to play non-Edison records on your Edison phonograph. Edison lost the format war of his time to Victor, by the way. He lost the AC/DC war, too (he was on the DC side). Huh.
One final point - one unintended benefit of DRM is that it may drive consumers to look elsewhere for music. The independent music scene is already benefiting from technology like myspace. Independent bands that offer DRM-free downloads and CD's will have an advantage that bigger bands don't. Which is good for music.
p.s. Richard Stallman recently wrote a letter to the Boston Globe on the topic.