One such game, online first-person shooter Combat Arms, was released by Nexon during the summer. The game's economy is based on NX Cash, where 1 million NX= $100. Combat Arms is the latest game released by the American publishing arm of South Korea-based Nexon.

Nexon's revenue model relies solely on in-game microtransactions, as opposed to ads or subscription fees. The company's games, which include Maple Story and Mabinogi (both MMORPGs), are free to play, and marketing manager Meghan Myskowski says the microtransactions don't affect gameplay, but rather "provide customization and personalization of your character. It enhances the experience for the user." And in the game, she adds, everything is assigned value.

The company sells prepaid cards in $10 and $25 increments; they're available at several online and brick-and-mortar retailers. The cash can be used to buy items in the game; the typical item value is $1. However, you can't cash out of the game, unlike some other in-game economies.

Virtual Economy Strengthens

Myskowski declines to give details about how usage patterns have evolved over the years since Maple Story was introduced in the United States in 2005. But she says the U.S. market had to get used to the concept of micropayments.