????It's not ads that make social gaming companies money, it's virtual pink tractors. Flurry Analytics says Apple's in-app e-commerce function is where developers can maximize bang for their buck.

????At the Social Gaming Summit in New York City today, Peter Farago, Vice President of Marketing at Flurry Analytics revealed some quick-hit stats regarding social gaming app makers like Zynga who use free-to-play business models and rely on features like virtual goods to turn a profit. The mobile apps analytics firm studies some 35,000 mobile developers.

????According to Farago, though many ecosystem players once assumed that ad revenue would be the best way to turn a profit, their real money maker has quickly become virtual goods, particularly for developers who cater to iOS. Turns out selling intangible items like say, tractors, fuel, and animals, is more profitable than once thought.

????Of the major platforms -- Google, Apple, Facebook -- developers make the most off iOS: between $14 and $20 per user per year. Google comes close with $18 per user per year, while Facebook lags behind with roughly $3 per user and Twitter claims $1 per user per year. (To give you an idea, if a social game claims a small userbase of say 1 million, that's already $20 million in revenue a year.)

????Here's a slide that shows the shift from ad revenue to virtual goods sales:

????Farago also revealed some stats about typical social gaming usage. Based on the companies Flurry tracks, social gaming has an audience of more than 19 million who spend over 22 minutes a day clicking, tapping, and swiping away.

????On average, gamers tend to spend between 2 and 5 minutes per gaming session depending on the type of game -- poker games tend to have the longest sessions, though smallest percentage of user retention over the long haul, while role playing games have the shortest sessions (hard core RPGs with 2.3 minutes and casual RPGs with 2.1 minutes), with an average of 2 or 3 gaming sessions a day regardless of the game.

????For kicks, here's a slide comparing how social gaming's audience stacks up against primetime TV programming like American Idol and NFL Sunday Night Football.