I think that this issue is being confused to some extent. Being a 22 year old gamer going through a teaching masters program I had the opportunity to work with a professor who was studying the learning potential of gaming. His hypothesis was that any game (Pac-Man, Grand Theft Auto, Dance Dance Revolution) could be valuable in creating an environment where students are engaged in learning. The schematics that students employ when starting a game that they are unfamiliar with are strikingly similar to retention of knowledge in the classroom. In fact, because the student is more likely to be interested in the video game over the text book it can be more effective. It isn't that a specific "learning game” is needed to improve student performance, it's what researchers and teachers can learn from how the student interacts and integrates with any game that is important.