Ezra Klein, in the May/June 2008 Columbia Journalism Review, examines The Future of Reading in an article that centers on the Kindle, but makes many observations that pertain to audiobooks. You can even watch a YouTube video where he discusses the issue, with a great use of The Little Engine That Could as an argument for content over medium. I particularly like this quote from the article:
"Pessimists have been predicting the death of books for what seems like forever. In 1894, Scribner’s Magazine published an article lamenting their destruction at the hands of audio. “Printing,” the author wailed,
which Rivarol so judiciously called the artillery of thought, and of which Luther said that it is the last and best gift by which God advances the things of the Gospel—printing, which has changed the destiny of Europe, and which, especially during the last two centuries, has governed opinion through the book, the pamphlet, and the newspaper—printing, which since 1436 has reigned despotically over the mind of man, is, in my opinion, threatened with death by the various devices for registering sound which have lately been invented, and which little by little will go on to perfection.One hundred and fourteen years later, printing is still around. But it did not win the battle against audio. Rather, the two entered into comfortable coexistence. Turned out that there were some things audio was simply better for. "
Image from www.cjr.org