David Pogue in the NYT talks about why none of his computer guides are available as e-books.
As one might expect, I have a rather complicated take on the issue, and one that is dominated by the considerations of the fiction and poetry markets, and not the reference or specialist nonfiction markets. I've seen a good case made that making novels available for free online can actually increase sales of the printed version, although I don't know if that would hold true for a computer guide. Why pay $30 for a "900-page behemoth" when you can find the one piece of information you're looking for in a searchable PDF online for free? Beyond the $30 that I'd rather keep, why should I devote shelf space to 295 pages that I'm not going to use, especially when they're in an archaic format with a semi-helpful "index" instead of a much more useful electronic text query?
The usefulness of a free e-version to fiction is publicity. A 300-page printed novel is actually a far more efficient delivery system than a 300-page reference book. If I enjoy a novel, I'm far more likely to read all 300 pages than I am to read even half the pages of the best reference book.
Pogue's more interesting point is that the value-added argument for books is more difficult than for music—there's really no equivalent of live performance in the literature world, especially not for the small author. You don't have to be Radiohead to make money off of live shows, but if you're not John Updike, you'll never make it on the lecture circuit.
At the same time, however, Pogue's own line of work belies his own argument. Even if he were to give his books away for free, he'd still be making money from his column in the NYT.
While copyright law is clearly broken (see previous posts on the topic), and, as an e-publisher, I clearly believe in the potential of electronic delivery to complement the printed book, copyright needs to exist in some form in order for literature to thrive. (Although I think that there are good indications that even if Pogue were to leave the market, that online free reference works would continue to exist.)