Shireling
A Servant of King and Country
I think the intent is to keep it simple enough to be approachable. Particularly given the nature of the setting, its sort of seems as if most nobility are somewhat similar in station and wealth, though there is certainly some disparity. Hard to accumulate substantially more wealth or govern larger swaths of land when everything is awful.
Regarding warriors - while perhaps an oversimplification in realistic purposes, its an adequate summary of the sort of characters people would want to play. No one, for example, has any interest in playing a pikeman - being a pikeman was patently horrible, required little "combat training" (relied much more heavily on sheer discipline and being able to hold formation, frankly), and, in terms of character classes, a pikeman wouldn't even count as a warrior.
We also have to remember that there is no real history of military tradition. There hasnt been a real war in hundreds of years, and generally armies are geared towards fighting nature. Some of the City Guard wield pikes and halberds to fight off large beasts, but they're generally equipped with longswords, bastard swords, and maces, and the sergeants may have a large weapon like a claymore or a war axe.
Vudu is also correct when he says that there isn't much of a difference between the nobles. There isn't a king, so there isn't really a hierarchy of nobility.