Of course a world where more people can get more books more conveniently is a better world. It is true that some individual authors may earn less in the new era, while others authors may earn more. But there is no reason to believe that authors as a whole will get less money. Indeed, as Amazon and other digital distributors gobble up some of the publishers' slice of the revenue, it's likely that authors will also get a share and see their total income rise. Beyond money, no book worth writing is undertaken for purely pecuniary motives. In the new regime it will be easier for writers to find readers and reach larger audiences. They just won't find them through the exact same set of middlemen who currently sit astride the pipeline.
Essentially, Yglesias believes that publishers are middle-men (at least as regards e-books) who don't add much value. Authors provide the product. Online venues like Amazon and Barnes & Noble and Apple provide the distribution. Publishers claim they're doing lots of marketing but Yglesias is skeptical they do that well:
When I was a kid, my father was a novelist as were both of my grandparents. So I heard a lot of stories about how useless publishers are at marketing books. Then I got to know other people who wrote books and they had the same complaints. Then I wrote a book, and their complaints became my complaints. But it's easy to whine that other people aren't marketing your product effectively. It took the Amazon/Hachette dispute to conclusively prove that the whiners are correct.Now, if you're George RR Margin, or indeed Matt Yglesias, is probably is true that publishers are moderately useless in terms of getting your book out to people. Yglesias knows journalists and runs a major website, and if he puts a book out himself he can let a fair number of people know about the fact. Martin is already a wildly successful novelists, so if he comes out with another book it is news and people will want to cover it.
After all, imagine a world in which publishers were good at marketing books. Then it would be almost trivial for Hachette to get what it wants out of Amazon. It could just not sell its books on Amazon! Unlike in the old days when it might have been inconvenient for someone who lived in a town with a Borders but no Barnes & Noble to go get a book that Borders didn't sell, it's trivially easy to click on some non-Amazon website to order a book. But you do need a customer who actually wants to buy the book.
The real risk for publishers is that major authors might discover that they do have the ability to market books. When George RR Martin's next iteration of the Game of Thrones series is released, I will buy it. If I can buy it as an Amazon Kindle book, I will buy it that way. If he decides that the only way people should be able to read the book is to get Powell's to mail them a copy, then I will buy it that way. And I am not alone. Nor is Martin the only author with the clout to not worry about the terms of distribution.
However, as someone currently self-publishing a book online (who wants to eventually publish through a real publisher) let me point out that while publishers are not very good at marketing books, non-publishers are generally a lot worse. When my sister's first novel was published by Balzer Bray (an imprint of Harper Collins) their publicity people managed to get early release copies into the hands of so many book bloggers and reviewers who liked the YA Fantasy genre that by the day her book came out it already had 1000+ ratings (most of them positive) on Goodreads and 100s of reviews. My own little publicity effort to get people to follow The Great War as it's published has thus far resulted in 174 page views of the first installment and 74 of the second.
Don't get me wrong, I'm intensely grateful to have the audience that I do, and I'm moderately confident that as I get more out there and convince my existing readers that the novel is good, I can build some word of mouth that will get more people reading it. But if that's how well I can do when I've been blogging for ten years, I think it serves to underscore that while the companies that currently exist in the publishing industry are definitely expendable, getting the word out about previously unknown authors is something that takes work which companies that specialize in that work are going to be better at than is the average author working on their own. And one of the reasons why Amazon lets you "keep most of the money" if you publish directly through them is that they do minimal work themselves to make people aware of your work. You keep most of the profits when you self-publish an ebook with Amazon because you do most of the work which either finds (or doesn't) an audience for your book.