At what cost?
Welcome to a negligible fraction of DMCA takedown notices. Amazon's same DRM powers also let them take away ebooks you foolishly thought you bought. Besides, isn't it a little bit crooked that those work whether or not the accusation is true? Take a stroll through Title 17 U.S.C. some time. It's not a pretty place these days. I suspect that many of the clauses therein are only allowed to exist because most of the population which is legally bound to obey them does not know about it. I didn't know how bad it was until I read it myself.
I also wish to add that authors are among the most vocal critics of the DMCA and DRM--partly because of their unfortunate effect on book sales. Books have historically been one of the most freely shared forms of media, and are the very origin of the concept of fair use--which the DMCA quite plainly shits all over. How many books have you found out about because somebody lent it to you? Books spread because their readership spreads them and thereby encourages others to get their own in hardcopy, because nothing feels quite as nice to read as a book in your hands--not to mention the little touches of clever typography that you tend to lose with ebooks. I mean, compare the Principia Discordia to its PDF analogue. I'm still ordering the thing in hardcopy because somebody lent it to me once and it's just way better than the PDF. DRM-infested texts have proven so unpopular with customers that many ebook publishers no longer bother; for example, O'Reilly's ebook sales more than double after they dumped DRM.
In fact, it's quite common for authors to put up at least part of a work entirely for free, then advertise that the entire thing is going to be a book. Sometimes, to make the thing more attractive, the author will add material to the book that's not on the website, but often it goes both ways; for example, both the internet version and the printed version of James Lileks' _The Gallery of Regrettable Food_ have things that are not in the other; the same is probably true of _Interior Desecrations_ and, in any case, everybody I know who's bought either had already read the majority of the material on the internet--and they bought them anyway. Alternatively, putting things on the website that aren't in the book encourages more people to visit the website. It works nicely both ways, and it's a popular tactic these days. Sometimes an author will put up a few books or a few chapters and then put the full version in print; if you really liked reading it, will you flinch at the idea of spending a few dollars to have the whole thing in your hands? And that's a thing to note--books usually just aren't very expensive unless the're rare*. If the price is right, more people will pay it.
I recall it created quite a stir when it became known that _Why's Poignant Guide to Ruby_ was going to be made into a proper printed book; I remember Ruby hackers waiting, salivating with one hand in their wallets, /to buy something that they already read for free/. Why? Because then they could own it; because then they could have it; because then it could be /theirs/. You don't get to do that with those obnoxious ebooks, software, and other media that you cannot own but merely license.
Authors want people to read their work--not shun it because it's bound in something nobody wants that tries to prevent people from treating books like books, and part of that is sharing them with your friends. When you buy a book, you /own/ it, and that's an awful nice thing these days, isn't it?
*Or they're recently published editions of textbooks, which obey their own horrifying system of economics because students have little or no choice in what they buy or for how much. I should be brief; that's a whole other hideous story. But who wants to pirate three hundred pages of poorly-worded calculus problems when it's $20 used anyway?