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With Android (s goog) gobbling up market share, it was just a matter of time before it took the lead in app downloads from Apple’s iOS (s aapl). That’s what happened in the second quarter of this year, according to ABI Research, which found that Android commanded 44 percent of overall mobile app downloads compared to 31 percent for iOS.

According to ABI, Android has much bigger install base compared to iOS, with 2.4 users for every iOS user worldwide. By 2016, that gap is expected to grow to 3:1. But even with the bigger footprint, iOS users still download more apps individually than average Android users by a 2 to 1 ratio. The ascendence of Android in app downloads isn’t completely unexpected considering Ovum already predicted that Android would take the title for the first time later this year. But it’s another sign that Android momentum is still going strong.

ABI also predicts that overall global app downloads this year will hit 29 billion, compared to nine billion in 2010. That figure is fueled in part by smartphone penetration, which is expected to grow to 46 percent in 2011.

Apple is still the No. 1 focus for most developers because of the fact that it’s a better place to monetize apps; Ovum predicts iOS will still generate more in paid download revenue in 2016 with iOS making $2.86 billion compared to $1.5 billion for Android. As I wrote about before, Apple customers are also more interested in downloading a wider variety of apps, which is helpful for developers.

But over time, the sheer numbers game along with some inherent differences in the Android platform compared to iOS, is helping turn more developer attention to Android. There are still more apps on iOS and the disparity is even more pronounced when you look at tablet apps. But more developers are starting to build for Android primarily taking advantage of its more open nature and some are seeing similar if not occasionally better results on Android.

Android still has some growing up to do to ensure that a wide number of developers can prosper on the platform. But it continues to gain momentum by virtue of its hardware sales growth and now we’re seeing that, in at least one metric, the scales have tipped in Android’s favor. The more important measure will be to see when Android generates more revenue than iOS.

That, as Ovum predicts, is still a ways off considering Android promotes more free apps. But with the growth of freemium apps that are powered by in-app purchase and advertising, we should see that gap close as well over time as long as Android continues to be a marketshare leader. But if Apple can claw back marketshare with the iPhone 4S and maintain its edge in tablets, it could take longer for Android to really overtake iOS in the app game.