There's an interesting article that was released by the analytics company Flurry discussing online gaming for mobile devices. After analyzing revenue streams from free vs paid mobile video game apps, they found free games with in-app upsells makes more money than paid games.

...we compared the revenue generated by pricing model, freemium vs. premium, among the top 100 grossing games in January and June of this year. Premium simply means charging for the download (e.g., $0.99). Freemium describes the free-to-play model, where the game is given away for free, and then the consumer can purchase virtual currency and/or virtual goods through in-app-purchases. Tracking over 90,000 apps with its analytics service, Flurry can measure the amount of revenue generated per ranked position in the App Store top grossing category. The chart below compares the proportion of revenue generated by each model.
I think there is a lesson to be learned here, and we can take that lesson to the bank!