That's true but even then it usually turns out badly. My point was that you cannot have a monetary system in which money can be found infinetly off of creatures or out of scrap piles. The only way a monetary system works is when there is a finite amount that is regulated by some means. Every large government on earth has a team of economists working on regulating their currency.
A system without a regulator never ends well. in most theme park MMO's it's fine since you only spend a short time at each level bracket and are expected to make substantially more the higher you get and once you hit the level cap you're supposed to be swimming in money. But in a freeform MMO you can't have that happening without the market becoming diluted and money becoming worthless.
Either way the system reverts back to bartering such as in pre WW2 Germany where it took a suitcase full of bills to buy a loaf of bread. So they used the colorful bills for wallpaper since it was worth less than actual wallpaper and they bartered for what they needed.
When the item becomes more valuable than the currency, the item becomes currency.