In Paul Graham's provocative "Post-Medium Publishing," he argues that we've rarely paid for "content," but rather for "form" — that's why a good hardcover costs the same as a bad one, and both are more expensive than paperbacks. As the newspaper and CD forms lose currency, their publishers argue that what we've been buying all along is the "content" and demand that we "continue" to pay for it online.
What about iTunes? Doesn't that show people will pay for content? Well, not really. iTunes is more of a tollbooth than a store. Apple controls the default path onto the iPod. They offer a convenient list of songs, and whenever you choose one they ding your credit card for a small amount, just below the threshold of attention. Basically, iTunes makes money by taxing people, not selling them stuff. You can only do that if you own the channel, and even then you don't make much from it, because a toll has to be ignorable to work. Once a toll becomes painful, people start to find ways around it, and that's pretty easy with digital content.
I think he goes off the rails in the next graf, where he talks about how writers can self-publish merely by uploading files; this commits the same error that he's upset about: confusing "publishing" and "printing."
I also wonder if St McLuhan might not object here, with something about the form being the content.