There's nothing new nor surprising here. The most popular on-line currency (actually, a set of currencies) of the Russian-speaking world, WebMoney, has its humble origins as an in-game currency of a similar, open-ended virtual reality: http://wmcity.ru
Although most of the virtual businesses turned out to be casinos.

Being in the right place at the right time, they fully exploited the comprehensive financial meltdown of 1998 in Russia to their advantage.

By now, webmoney is by far the most accepted currency among Russian-speakers and their operators can afford to buy banks in the baltic states for the sole purpose of conforming with EU regulations. They have their own ATM (debit-) cards, and most Russian cellphone and satellite TV operators accept payment in their currency as do large on-line retailers, like ozon.ru (the largest Russian internet-bookstore).

Legally, they are an escrow service and typically, their currencies are 100% backed in cash at all times.

P. S. My own project, ePointSystem, has also been initially developed as an in-game payment system for an open-ended on-line game. The game project was pretty much abandoned, but the payment component lives on.