Where’s the money in mobile apps? According to app analysis firm Flurry, it’s in virtual goods, not ads.

In a post on the company’s blog, Flurry notes that mobile virtual good account for 80% of revenue from iPhone and iPad apps, which include such microtransactions as new songs for games like Tap Tap Revenge 3, or new weapons, accessories and levels for other types of games.

Stats like this are what’s driving the virtual goods market. Mobile and social game developer Ngmoco, which claims 40% of its revenues come from virtual goods, was acquired earlier in the week by DeNA for over $400 million.

Michael Pachter, videogame analyst at Wedbush Morgan Securities, thinks social gaming revenue will increase from $1.6 billion this year to more than $4 billion by 2013.