Apple's App Store is doing quite well and by extension its developers are doing well too.

Since its establishment in 2008 the App Store has generated more than $120B in developer earnings - that's without Apple's own 30% cut of the revenues.

The App Store is growing faster than ever, generating more than $30B in developer earnings in the last 12 months alone.

The revenue figures for developers' earnings include downloads, in-app purchases and subscriptions, meaning some developers might earn even more from in-app ads.

Source