Let's suppose that one day I wanted to listen to some Stairway for some dumbass reason. Maybe a great geetar solo or whatever. As everyone should know by now, Stairway to Heaven has messages from Satan himself embedded backwards in it somewhere. So let's suppose that I set out to find them.
In parallel universe number one I choose a vinyl LP. It is shiny. I reverse the motor in my record player. I place the pin near the middle of the record. I sit back and enjoy.
In parallel universe number two I choose a cassette tape. It is less shiny, but more compact. I fast-forward through the tape, add some resistance to the circuit powering the reverse capstand motor (doing some calculations first), press "play" and then "rewind". I take in the sweet words of Satan.
In parallel universe number three I choose a compact disc. It is really shiny and sort of compact. As a frisbee, it doesn't fly all that well. I use some software based on the CD Paranoia library to capture the raw PCM data to my hard drive, write a short C program to reverse the order of samples in a PCM file of that format, run that program on the captured data and play back the reversed PCM data with aplay or similar. It's a bit of work, but worth it for digital quality.
In parallel universe number four I choose to buy from the Napster subscription service. It lets me download just Stairway! Unprecedented freedom! But wait: it doesn't let me at the sample data. It only gives me "play", "pause", "stop", "skip" and "previous". Short of getting hired at Napster I'm out of luck. Well, sure, there's the "analog hole". It'll be closed soon enough.
What's happened here? I've gained over the years freedom of venue in my listening from the more portable formats and players. In the end they gave me the freedom to download individual songs but took away the freedom to see the actual data of the song. Why did it happen? Because the record companies don't trust me to respect their copyright. That's mildly insulting, but they don't really have any reason to trust me. Good security is almost always deny-by-default, and if they don't know me and my motives personally they can't trust me.
But it goes both ways. To buy from Napster or any other DRM-based system is to put my trust in the company. It's in my interest to play the music that I've purchased, but I can only do that if my interest intersects with theirs. Will this be the case? What if I want to play it on a computer running GNU/Linux, Plan 9 or BSD? They don't care, unless all three OSes go big. What if I get an iPod (it's a stretch, I know) and want to play it on that? Not going to happen. What if I want to play it backwards? Ha! Why should I ever trust that what's in their best interest is going to also be in mine? The fact that it's ever the case is an unreliable coincidence.
So if media companies want my money, they have no choice but to trust me. Because after my experience in parallel universe number four I sure as hell don't trust them.
Curiously, when you think about DRM from the angle of trust, a slightly different case is Apple's iTunes Music Service. It was a response to the success of peer-to-peer file sharing, and has successfully made money competing with free (but often illegal, if the files shared are copyrighted) sources by offering something that to some people is worth the money. That has always been the spin, at least, but that's also what many users say and the general attitude shown by Apple: they've fought the record companies over the right to set their prices, for example, to retain their vision of the service. And what does Apple allow you to do with your iTMS tracks? Burn them to a CD! Unencrypted! They trust you! Or, at least they trust that they can convince your friends to buy the songs themselves on iTunes instead of copying your CD. It's not perfect; transcoding will result in poor quality, but that's an artifact of the original lossy compression rather than the DRM. But Apple doesn't trust you completely: you still have to use their closed-source software to decrypt the files, which locks out people running any OS but supported versions of Windows and MacOS. This gesture of mistrust means that I still would rely on Apple to get at my music the first time, which punts iTMS off of my radar. Also, the lossy compression makes transcoding to some open format for efficient storage and playback on my computers that can't run iTunes painful, which punts it even further.