I have asserted on several occasions (such as in papers given at Society sessions at the International Congress on Medieval Studies) that the "standard" setting of fantasy fiction is one that is amorphously European feudal (typically High Middle Ages or Early Modern English in overall shape). That is, governmental authority is vested in a single monarch whose rule is supported and vested in a number of subordinate nobles who receive land and authority form the monarch, but there is not much in the way of formal distinctions. Perhaps one or two gradations of nobility are identified subordinate to the monarch, but only those. How this manifests in Tolkien, I mean to discuss in my contribution to the upcoming Society volumes, as does how it manifests in Robin Hobb's Six Duchies novels. It can also be seen in the structure of Gernia, the milieu of Hobb's Soldier Son trilogy that I discussed in a paper given at the 2010 South Central Modern Language Association conference and Helen Young discusses in a recent article; a number of ennobled lords serve a king, with only seniority distinguishing them in formal rank. Katharine Kerr's Deverry novels offer a bit more detail in the nobility of Deverry; there is a king and some princes, supported by those styled gwerbret, tieryn, and lord, in descending order of precedence. George R.R. Martin's Westeros is a bit more detailed, with bannermen sworn to various lords and expressly described as such, and some lords further ennobled as Wardens of large regions of the kingdom. Even so, none offers as much distinction among its noble ranks as does the exemplary English/British structure of nobility, with its overlapping ranks of duke/duchess, marquess/marchioness, earl/countess, viscount/viscountess, and baron/baroness, and gradations of seniority within each. The typical fantasy kingdom's relatively flat social hierarchy stands in contrast to a system forming a complex and complicated order of precedence in which issues of entitlement and privilege become means to exercise authority and their denial a means to offer insult. Why it should do so, why it should gloss over hierarchical distinctions with which the medieval mind (insofar as such a thing can be said to be) was quite concerned amid so many invocations of the medieval bears some explication.
One possibility for the leveling of the formal social hierarchy is the recognition that such structures do not obtain in the daily lives of the readers. The United States is a major market for fantasy literature, and while nobility and gradations of it are seen as prototypically "medieval," so that they have to be included, a strict social hierarchy in which people are born into places from which they may not ascend except in exceedingly rare cases runs counter to the prevailing cultural narrative (as it is reported; as it is evidenced may be a different matter entirely). Too, as I note in an earlier post, formal gradations of nobility in government are expressly prohibited by the core of United States law (US Const., art. I, sec. 10), so giving too much attention to them comes off as "un-American," something generally perceived as to be avoided in the US. But that does not account for readers in the UK, which remains a monarchy, or the various Realms of the Commonwealth, which ostensibly acknowledge the sovereignty of a monarch; in both cases, however, the peerage and royalty are largely nominal and ceremonial. They little affect the daily lives of the people, except perhaps in disruptions to traffic patterns and in providing convenient foci for ideations of celebrity. Thus, while it may be that the flattening corresponds to an anti-hierarchical sentiment among US fantasy readership (and, perhaps, that of other countries that rebelled against such structures or who peacefully but no less decisively removed themselves from royal and noble dominion), it may be a lack of importance or a lack of familiarity that prompts it for those readers who live in the various English-speaking countries in which monarchy is still in force. In each, the medieval is seen as "needing" nobility, but that nobility is minimized so as to correspond more closely to contemporary ideologies.
The idea does, however, leave open the question of Tolkien's flattening of his own noble hierarchy, since, as a medieval scholar and a man born in a British colony late in the Victorian era, he would not have been quite so much subject to the lessening of noble relevance as are those who follow him and those who write as citizens of nations that have repudiated structures of hereditary nobility. Yet his scholarship might provide an answer. Tolkien is noted for having been an Anglo-Saxonist, and the Anglo-Saxon noble structure is much flatter than that imposed on England by the Normans and that which developed in the succeeding centuries. A king (or seven, but who's counting?) is served by those styled ealdormann (alderman), eorl (earl), and thegns--and ealdormann and eorl seems to have been more or less interchangeable. Tolkien's amply attested source material, then, exhibits a relatively flat noble hierarchy, so that it is not to be wondered at that his recapitulation of it does so, particularly in his mimetic-of-the-Anglo-Saxons Rohirrim and his earlier overarching project to develop a distinctly English mythical history or pseudo-history. Since Tolkien does serve as a foundational figure to fantasy literature (as the Society happily acknowledges), it follows that later fantasy authors, looking back to him, would emulate his less-detailed scheme of noble gradation. Perhaps the coincidence of mimicking Tolkien and addressing the expectations of readers who demand "medieval" setting features without violating their current social contexts (much and overtly) accounts for the continued reduction of noble and royal title from their proliferation in England and elsewhere to their appearances on the fantasy literature page. And perhaps there are other factors contributing to the non-distinction than those for which I can account; further discussion of them would be welcome, as would further discussion of the possibilities this piece suggests.