To be considered currency, a coinage only requires the agreement of the coin holders to use it as such, in other words a marketplace. Tyrian NPCS reward/pay our Heroes with Karma and our Heroes then use it to purchase goods. It is distressing that a builder of Tyria does not consider Karma legitimate Tyrian currency. The Karma currency replaced the more traditional quest reward system giving us more freedom in adventuring but did not redefine the marketplace effect of NPC rewards.
“No! You can’t eat the ones that talk!
They’re special! They got aspirations.”
Finn the human