[Poppa1956]

Bear in mind the editorial outlook of the WSJ is more than a little pro-business. They support policies and decisions they believe will protect and help grow businesses.
It is their view, and that of many publishers that DRM is preventing them from losing money via theft.
Previous to the WWW, a major concern of publishers was photocopy machines in libraries and schools. Now, in many countries anyone that can scrap together a few sheckles can buy a computer, and an all-in-one printer/scanner/copier/fax/espresso maker (JK, they don't all have FAX) and make pdfs, and make them available via bit-torrent. (But that is unlawful, so don't say I recommended it.)
Until only a relatively short time ago, if you wanted a public domain book, you needed to find a library or a book store. Obviously, that is no longer true. But B&N, Amazon, (and soon) Borders, et al. are trying a digital variation of that model. I believe they will have a market share for a long time, even of PD books.
For some people, it is worth the cost to purchase PD eBook from a retailer, and have it automatically download to their devices, and much too difficult and time consuming to search for said book, download it, and sideload it. Nor will those same people care whether the book has DRM or not.