Look, praguepride, you're welcome to not care. You might not think its fun. DF isn't just for you.
However, DF at its heart is a management game. Similar games have historically involved economic subgames as the or a major focus of gameplay.
There is abundant evidence that economic 'warfare' is a viable game basis. Sid Meier's RRT spawned numerous sequels and knock-offs, and its immediate successor RRT2 made the top 100 games of all time.
You're welcome to say its not fun for you, but its obvious that it would be fun for a lot of people. Especially since it goes hand in hand with the management style game DF already is.
Ok, lets clear up some willful stubbornness or clear lack of understanding on your part.
Imagine you get dropped onto an obsidian map. There is nothing but obsidian, and the occasional gem. Your only source of income to buy all those metal ores you need comes from those little mugs and knick-knacks you dump on wandering merchants. Now suddenly they say "no more obsidian items"
What's left? You're s*** out of luck and what is ordinarily a rare and beautiful thing (all...that...obsidian!!!) has become a horrible curse because you built yourself onto a mountain.
With the exception of raw obsidian and obsidian blocks, the fact that something is made of obsidian should not be the sole determiner of demand for it. (And demand for obsidian stone and blocks should be large and relatively inelastic with respect to supply.) If you're selling a stone mug, its still a stone mug. They may stop paying a premium for obsidian stone mugs if you flood the market with obsidian stone mugs (obsidian is only more valuable than other stone as long as its rare), but they won't stop buying stone mugs unless you sell enough to flood the entire mug market. And there are a lot of other things you can make with obsidian (various types of furniture, mechanisms, etc...) which have their own S/D relationships independent of mugs.
Plus S/D doesn't work if you actually work to control prices. Look at what Japan's done to the US. As part of their business strategy they've completely ignored S/D pricing and kept their prices steady for decades.
I'm not sure what exactly you're referring to here. Japanese imports have been provenly priced below actual market value before, hence the crazy ebay prices on things like console systems at first release, because the company didn't make enough for demand at the price they were sold at. This means that japanese goods most certainly follow S/D in the market - goods sold below value will be resold by buyers to others who are willing to pay more and can't get one.
I'd love to know what prices you think they've kept steady for decades. Vague allusions to things that make no sense don't convince anyone. (Japanese car prices have not held steady. Console game prices have fluctuated. TV prices have varied. Etc...). Also, Japan is not a monolithic entity. Japanese companies make pricing decisions, not the japanese government.
S/D does not auto-dictate prices or resources or anything. Heck, look at "fad" items like Pokemon or Beeny Babies. There was no demand before the product. Someone somehow stirred it up after the supply was there.
Its called marketing. And there was certainly demand for the category of product (eg, 'toy', 'stuffed animal') long before their were pokemon or beanie babies. Successful marketing increased demand for those particular products.
Finally, there is a philosophical rule that comes to mind (I don't know the name, don't ask) but basically you cannot model a system if you are not outside of said system. It's the issue we're running into with programming A.I. We don't really know how intelligence works as is, let alone trying to model it on a smaller scale. An ant in an ant farm has no idea what "glass" is. It has no idea that it is not on the ground but on a shelf. Then ask said ant to model it's surroundings and it will be wrong and incomplete, because the ant can never see the whole farm from beyond the glass walls.
How does this even apply? Determining rational supply/demand relationships for goods shouldn't even be hard, since we know their shape and have some idea about how elasticity (read: slope) should vary by good type.