All this is so I can quote a few passages from a battle between the Romans and the Insubres, in 223 BCE:
"They [the Romans] had learned from previous battles that the Gauls are at their most dangerous in their first onslaught while their ardour is still fresh, and also that because of the way their swords are forged, as has already been mentioned, it is only the first slash which takes effect. After this the edges are immediately blunted and the blades become so bent both lengthways and sideways that unless the men are given time to straighten them with the foot against the ground, the second blow has virtually no effect."
The Histories, Book II.33
In my Penguin copy, there's this footnote:
"The same details concerning the soft edge of the Gallic sword are found in Plutarch's account of Camillus' victory over the Gauls in 377 B.C.; it may have become a traditional legend."
Then, later in the same chapter, Polybius writes,
"As soon as the enemy [the Gauls] had delivered their first sword cuts against the shafts of the spears and so put their weapons out of action, the Romans closed with them and rendered them helpless by leaving them no room to raise their arms to slash; this is the stroke which is peculiar to the Gauls, and the only one they can make, as their swords have no points. The Romans, on the other hand, made no attempt to slash and used only the thrust, kept their swords straight and relied on their sharp points, which were very effective."
Such fascinating detail! The design of the broad sword vs. the slashing swords of the Gauls, the manner in which the Romans could press in on the Gauls and keep them from even swinging and the softness of the metal that the Gauls could smelt. This last is the most interesting to me, because once again we come back to the subject of orcs.
Humans, as we know, are part of an extensive culture - a necessity, since the players are bound to play some sort of humanoid that moves from place to place, expecting to be able to buy goods, stay at inns, use roads for travel and so on. This unification means that technology is shared, so that developments spread throughout the geo-political culture.
Orcs and other humanoids, however, are necessarily isolated. They have no trade, which means that unless a particular group of orcs happens to be sitting on a good supply of soft coal (hard coal could not be easily mined until the 18th century, after the development of harder steels and steam power) as well as iron, limestone and a hardening metal such as nickel, manganese, chromium or tungsten, we wouldn't find a society that could mass produce good metal for weapons. Even if those materials did exist, there's no guarantee that the masters in house were clever enough to have developed metallurgical skills to match the highest degree of human-based technology.
In short, the orcs simply wouldn't have weapons to match human weapons, just as the Gauls did not have weapons to match the Romans. It's no good, either, arguing that the orcs could have found enough weapons to sustain them, for as we know from both Polybius and Livy, the Gauls won plenty of battles against the Romans and this didn't help them.
See, the problem with found weapons is that the use of the weapon is dependent upon the individual being trained in the use of that weapon. The Gauls may have found plenty of Roman broadswords, but this didn't make anyone among the Gaulish tribes suddenly professional at being able to manipulate and effectively use the weapon once they had it. See, there are muscle groups that need developing, a stance to be adopted, techniques, a way of thinking about the weapon and so on - and these things are NOT self-evident. Gauls might have tried, but they would have soon found the Roman weapons were too heavy in all the wrong ways - even if the actual weapon was lighter, without those muscle groups it would have felt wrong.
Suppose that we have an especially developed group of orcs who luck out in the mineral department so that they have everything they need. Let's also say that there's a really brilliant orc that stumbles upon the secret of an improved forged iron, making perhaps the best iron in all the world. It's a possibility, right? Why not simply say that?
First of all, because obviously not every orc clan in the world can be so lucky - though we can expect a DM to cheat and suppose they might be. With a genius orc iron founder in every clan, yet. It still doesn't fly, for one simple reason. Technology does not stand still. Whereas today the orc founder comes up with something really original, the human culture doesn't depend on just one genius. It jumps forward any time someone, somewhere, comes up with an original thought. The orc clans in the traditional vision, however, are not communicating with each other. They're in dungeons, deep underground, isolated and hardly trading thousands of tons of materials with other clans, or sharing knowledge from one clan to another as quickly and easily as humans are.
No matter how you look at it, the orc technology is going to lapse, and when their swords fall against the swords of humans, and their friends elves, dwarves and so on, those orc weapons are going to fail. They're going to break or bend, and then the orcs will go where the Gauls went.
My solution was to make the orcs a huge culture, with huge territories, where they numbered in the millions and traded among themselves. I also felt that in times of peace, the orcs ought to be able to trade with humans and vice versa. Why not? We trade with genocidal nations, even where the leader is a cannibal, all the time. Why not orcs? Wall Street wouldn't care.
Most, however, will simply ignore all this, giving orcs and other subterranean humanoids magical powers over the manufacture of iron weapons, which appear mysteriously no matter how many levels down we go - while no evidence of a forge - or a chimney leading outside from that forge - ever makes an appearance.