Which gaming platform first introduced a successful virtual currency system for purchasing digital content that became a model for the industry?

The gaming industry has transformed how we think about retail transactions. Virtual currencies and in-game purchase systems have created entirely new economic models that blur the lines between digital and physical retail. This question tests your knowledge about a pivotal moment in gaming retail innovation that forever changed how players interact with virtual goods and services.

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Microsoft's Xbox Live with Microsoft Points (2005)
PlayStation Network with PSN Wallet (2006)
Nintendo Wii with Wii Points (2006)
Steam with Steam Wallet (2010)