Whenever we see adventurers in pre-WotC D&D games, we see them as outsiders. The adventurer and the outsider are essentially the same category within these earlier games. Adventurers are not integrated into society -- they actively remove themselves from it. They are as integrated into their societies as their High and Late Medieval counterparts, the mercenary (as a good exemplar of a mercenary-adventurer take Sir John Hawkwood), which is to say not at all.
Adventurers begin life refusing the normal social order of the setting. They will not be farmers, they will not be merchants, they will not be bakers, or butchers, or blacksmiths. They have run away from their fathers, refused the allure of steady apprenticed work, or perhaps have no other place to turn (ah, the ubiquitous adventuring-orphan). They are literally outside the social structure. Adventurers have no place in society, not even as cotsmen or wandering laborers do.
Furthermore, they are travelers. They go from place to place, itinerating over great distances. They cross county, kingdom, and wasteland without staying long in any one place. Anyone who lives in a single region for long enough will eventually develop ties with the locals, both legal and emotional. These ties are weak in terms of adventuring parties unless they decide to settle for good and begin the next phase of their development. As we all know, the adventuring arc takes outsiders and transforms them into insiders: lords, landed mages, temple-founders.
But in their formative, roving years this is unlikely. Adventurers seek a way of living that may seem senseless to others. Rather than accepting the stead realities of every day life, adventurers put themselves and their companions in constant danger in the hope of a reward that is greater than their station. In the 10th Age, this makes them alternately feared, loathed, and loved depending on the person you ask. This was also true of the original D&D settings, as I'm sure all you OSR oldies out there know: adventurers are grave robbers, thugs, brutal murders but they are also rock-stars, heroes, and Robin Hoods.
The semantic category of the adventurer is one that defines itself in opposition to the "center," to the stable and well-known relationships of society. An adventurer is one who, by definition, seeks "adventure" outside the confines of what is safe. If the city and the town are the center, then the liminal regions are the bandit-filled forests, the ruins that lurk at the edge of known territory.
The adventurer re-performs the essential cooked/uncooked act of Levi-Strauss' theory: he must leave the stable and sensible territory for the violent wild where he will garner riches and, sometimes, self-knowledge before returning to the land of the cooked. Of course in, say, a western, the hero never becomes fully "cooked" -- he is a violent killer forever who is so dangerous that he has to move on to the next town. But in the world of D&D, the killers of yesterday are the lords of tomorrow, and that is not so far from the military truths of the actual Middle Ages.
Indeed, adventurers are other. They have placed themselves outside the careful mechanisms of society to advance by the short road. Where a farmer may slowly build up money to hopefully one day purchase a second farm and rent it out to some other poor peasant (a dream which, of course, could be taken away from him by one good orc raid or terrible growing season) adventurers bypass all of that. They don't steadily advance along a slow route towards some bourgeois fantasy of burgerhood, or even to the accepted ranks of lesser nobility.
They refuse to do knight-service and fight only in campaigns when their lords call them, living the rest of the year on their farms. They refuse also to run shops and generally go about all the little actions that people who are integrated into society take in order to better their lives. Adventurers are a form of gambler (that may be mixed with doing good or not) who seek the next thrill. Like the soldier who comes home from a war and finds that he misses it, adventurers are often thrill seekers willing to bet their very lives on their next delve.
Of course, not all adventurers can easily fit this mold and you may have players (or DMs) who want to explore relationships that occur within society long before the adventurer's set tenure as an outsider is technically up (level 9ish) and that is possible as well.
Even barring all this theoretical hocus pocus and jargon, the adventurer is clearly positioned outside his society. This is a functional concern as well as a theoretical one; if adventurers weren't outsiders, they would be engaging in the every-day humdrummery of medieval life, which is certainly not what D&D was made for. That being said, I find this aspect very interesting and my long-standing attempts at integrating some of the kinds of "adventure" (insider-adventure, I would call it) from Hârn speaks to my desire to have insider- and outsider- "adventurers." To that end, there will at some future date come an article about insider adventuring and how you might conceivably set out to achieve it even using a system so focused on the outre as D&D.