Thor Power Tool Company v. Commissioner, 439 U.S. 522 (1979) was a United States Supreme Court ruling which changed the way companies are allowed to depreciate their unsold inventory. Thor's inventory was overestimated, and was written down to scrap, but it did not immediately scrap the items or sell them at reduced prices. Thor treated the write-down of excess inventory as an adjustment to closing inventory increasing the costs of goods sold and reducing tax due. Reducing tax liability may not have been the drive behind Thor management's incentive to reduce inventory, but a welcome by-product; new management may have wanted to reduce the previous year's profits so as to seemingly increase their performance in the following year.
An unforeseen side effect of this decision was that it became less profitable for publishers to keep slowly but regularly selling books in print (their backlist). Some argue that this has made it harder for midlist authors to make a living because books tend to be remaindered or pulped and go out of print more quickly.
In other words, a de facto change in the tax laws concerning inventories made it profitable to pulp unsold books earlier and this has had an adverse effect on authors who have slow but steady sales. As Levine noted to me, this ties into the whole issue of digital technology. On the one hand, digital technology makes copyright de facto obsolete, and it can make it harder for creators to recoup their investment because the market may be flooded with cheap copies quickly. This is what the pro-copyright forces argue (so therefore we need draconian copyright laws to overcome all this). The basic facts are true, but there are many facts that go the other direction. This is one of them--by selling electronic or print-on-demand copies directly to buyers authors don't face "early liquidation" by publishers.