hong said:
People who have +8 to Craft (armoursmithing) are not, by any means, the "bulk of humanity".
Ok, then. Let's reformulate.
IMC, most human artisans with a specialty generating a substansial income, such as armoursmiths or weaponsmiths compared to blacksmiths, are likely to be experts or very dedicated commoners, aquiring the feat Skill Focus in an ealry stage of their career. 3 or 4 ranks at 1st level + Skill Focus in the craft you practice every non festival day of the year + an intelligence score around 11 (standart array) or 13 (non-elite array) : that's a quick +6 to +8 bonus.
IMC, most low-level armoursmiths (1st or so), are engaged in the most common tasks of their trade : usually crafting mail. As they mature, they probably start to assume the task of completing whole armor. Then, advancing in their trade, they engage in the more diffucult task of crafting heavy armors with complex articulations, i.e. banded, plate mail, full plate armor.
This evolution is, IMHO, can pretty much be described as aquiring experience, which happens, in D&D, to turn those armoursmiths into higher level Commoners or Experts.
Like you stated : the bulk of humanity is probably around 1st or 2nd level.
But D&D rules, notably with the city population generator, assume we encounter a fair number of high level Commoner or Experts (in many cases, a Commoner in the highest-level invidual of a given town).
I just suggest that the more complicated tasks, such as the making of a full plate armor compared to that of a chain mail, is likely to be the trade of the most advanced individuals. I happen to think these higher level commoners and experts are the crafters and traders of the most advanced and profitable businesses around.
Especially when heavy guild systems, such as those described in most D&D settings, tend to protect and restrain that business to specific and advantaged groups of individuals.