Is this a question or just smug self-aggrandisement?
Dude, I love asian-inspired campaign settings, and your product looks pretty cool, but don't insult our intelligence.
Anyway, for the record I like my fantasy settings to be populated by fantasy cultures, not real-life historical ones. So while I'm a big fan of cultural window-dressing borrowed from real-life history, I don't need all the bits and pieces that make classical D&D adventuring (tomb-raiding, killing monsters, looting their corpses, and socially independent, self-interested itinerancy) more trouble than it's worth.
So while I love Samurai, what I really want in my game are "samurai" - blokes with a katana, a wakizashi and a pair of sandals, but who have no issue with carrying money, touching dead bodies or gambling with riff-raff down at the tea house.
Obviously I'm not too interested in immersive roleplaying - I'm a storyteller, not a method actor - so the constraints on social interaction imposed by historical representations of one or another caste system don't really appeal to me. The kinds of games I like to play (mystery/investigation/frequent violence) are best facilitated by a fairly modern, egalitarian version of historical fantasy cultures.
This ties into something else that bothered me-if one player has a samurai character, for example, can he really go off with the other party members, or is he stuck doing step-and-fetch quests for his master all the time? Does acting with "honor" mean violating your alignment? Why would anyone say an insult, given that it would provoke a feud? Why would anyone act dishonorably in the first place, if the culture places such a heavy stigma against violating the code of ethics?
Reading through the original
Oriental Adventures, I found that the lengthy section on honor added little of value to the game and in fact really seemed to suck a lot of the fun out of it, if you're stuck observing all these little niceties that aren't much fun to begin with, especially when NPCs act "dishonorably" with few negative consequences.
Instead, play around with the traditional tropes and use them to your advantage. Maybe that samurai isn't devoted to a master, but rather a philosophy inspired by real-life Bushido. The samurai seeks to live his life according to those principles, which grant him tremendous power and skill. At the same time, he acts as an adventurer to gain honor and fame for his clan, as well as treasure to increase its social standing. Just as nobles in an Occidental culture might seek to prove themselves worthy of the family name through their heroic deeds, high-born Oriental people might find the adventuring path a way to increase their house's standing and glory, while proving themselves worthy of their ancestors' legacy.
Against such considerations, any possible stigma against associating with the lower-born classes suddenly counts for much, much less.
What's that Brahmin doing wandering around like a commoner, ransacking old ruins and seizing treasure, when he has priestly duties to attend to? You might ask the same thing of any typical Western cleric-why does his temple allow him to spend all his time wandering around and fighting monsters, instead of preaching to converts and holding regular services?
The Brahmin and the Western cleric are adventuring for the same reasons-their faiths state that, in order to attain true spiritual purity, they must travel the world to better understand it, fight on behalf of the faithful, and seek to inspire others to join the faith. One heroic deed is more effective at inspiring people than a thousand fiery words. More material considerations are at hand, too-the different faiths compete with one another for followers and prestige, and, sadly enough, even religions have bills to pay. That extra wealth the Brahmin or cleric gains in his travels could mean the difference between prosperity and ruin.
Western, Conan-style barbarians set out into the world to prove their manhood...so why can't a monk, magic-user, or ninja do the same thing, travelling the world to seek enlightenment? All social classes and races may have potentially valuable knowledge, and refusing to associate with people in a lower social strata would be seen as foolishness. The parties formed by Oriental adventurers can be just as racially and socially diverse as any Occidental party, and no one will blink an eye.
These are just some examples, but it shows how one can modify aspects of Oriental culture to create an internally consistent setting that still allows for the basic aspects of D&D that Snoweel mentions. If we're going to mess with the social structure of Europe in order to make the fantasy cultures based on it fit better with the game, I don't see why we need to be any more accurate with the Oriental ones.