This is an excerpt:
"Let me rephrase, it’s a radically subsidized economy. I’m not speaking of removing all subsidization, I’m talking about not flooding the game with gold.
NPC shops are a subsidy, obviously, as they buy stuff for which there is zero real market. In a non-usage game, we could say they subsidize the gameplay of adventuring (which gives you lots of useless stuff) or pursuing your chosen playstyle (like say, crafting stuff that nobody wants, because it’s how you have fun).
In a game like UO, which is usage based, the NPC shops are rewarding macroing and the pursuit of skill points. They’re not even rewarding having fun necessarily. They’re just a gold spigot."