Back during the golden age of the soc.history.what-if newsgroup (which is to say, back when I was regularly posting there, roughly 1999 - 2005), the forum was plagued by a rather peculiar internet troll. As is often the case with internet trolls, he appeared under a series of different pseudonyms, as he would be banned for his trollery, and then return under a new name (and usually a new ISP). However, despite his many nyms, he was known among the forum's regular posters by his original pseudonym: Quonster. As is also often the case with internet trolls, Quonster was not there to cause random disruption just for the hell of it. Quonster had a Cause, and for reasons beyond comprehension he meant to use shw-i to propagandize for his Cause.
In Quonster's case, the cause was absolute monarchy, with the attendant institutions of a powerful landed hereditary aristocracy, and a rigidly defined caste system based on aristocratic lineage (or "pedigree" as Quonster put it). Quonster was fixated upon Wilhelmine Germany as the perfect exemplar of his ideal society. Like many other people with a poor understanding of the society of the European Middle Ages, Quonster fixed on the word "feudalism" as a label for absolute-monarchy-with-attendant-hereditary-aristocracy, and used it incessantly (in fact, one of his many pseudonyms was "Feudalist").
This is all by way of introducing this week's featured article on the Sobel Wiki: the Bloody Eighties, a period of anarchy and social upheaval that swept Europe in the early 1880s. In the Sobel Timeline, the failure of the American Revolution was followed eleven years later by the failure of the French Revolution, thereby avoiding the political and social upheavals that Europe experienced in our history from 1789 to 1815. However, in the Sobel Timeline, the upheavals were not prevented, but only delayed for ninety years, with the fall of the aristocratic order finally taking place during the Bloody Eighties.
When Sobel talks about the traditional aristocratic order in his chapter on the Bloody Eighties, he refers to it as "feudalism" in exactly the same way Quonster did, to mean absolute-monarchy-with-attendant-hereditary-aristocracy. This might be evidence that Robert Sobel, specialist in modern American business history, was too tightly focused on his own speciality to realize that feudalism doesn't mean what he thinks it means.
On the other hand, it's important to distinguish between our timeline's Robert Sobel, and the Robert Sobel who is native to the Sobel Timeline, and who is the putative author of For Want of a Nail. Alt-Sobel, as we might call him, is a very different person, with a very different background, from our own Sobel. He can be thought of as the fictional narrator of Nail, with our Sobel engaging in the novelist's craft of writing the book in the persona of this fictional narrator.
In a review of Nail published in the New York Post, Martha MacGregor noted that the book "is a spoof, and the spoof is in its form -- too many footnotes, too much bibliography, too dense detail." So it's not unreasonable to suppose that Sobel was having some fun at the expense of the author of this tediously written tome, by having him misunderstand what feudalism actually was.