It had to happen eventually, what with 500,000 Android devices being activated every day around the world. The Android Market has finally surpassed the iTunes App Store in app sales, generating 44 percent of all app downloads for Q2 2011.

The numbers come from ABI Research, as reported by Pocket Gamer, and find that in the second quarter of 2011, the Android Market finally topped Apple’s App Store, which pulled down 33 percent of total app downloads for the period. While Android has enjoyed a greater user base than Apple’s devices for some time now – there are a ton of Android smartphones and tablets, while Apple has only the iPhone and the iPad and (formerly) was limited to two carriers – it hasn’t been able to surpass the app downloads of Apple’s platform. The iTunes App Store still has more apps available than the Android Market, but that’s not likely to last, either.

ABI Research blames the ubiquity of Android devices for the slowly increasing numbers, and it’s not surprising. There are just more Android devices out there, and that translates to more app demand, and therefore more downloads. ABI points to Android’s free, open nature, which is the reason it’s available on so many devices to begin with.

One wonders how that might change going forward as more device manufacturers start having to pay to use Android. But they’re not paying Google, they’re paying Microsoft for the use of patents it owns that relate to mobile technology. Microsoft has inked nine licensing deals in four months with Android device manufacturers, most notably with Samsung, Android’s biggest partner and currently the leader in smartphone sales on the planet.

Meanwhile, the last quarter has been something of an anomaly for Apple, and it might be about to come out swinging against Android. The run-up to the release of the iPhone 4S saw Apple’s iPhone sales decline about 9 percent in the quarter ending on Sept. 30, dropping to about 17 million sales from the 20 million units sold during the same period the year before. By comparison, Samsung is believed to have sold somewhere between 22 million and 26 million smartphones during the same period.

But Apple saw record-breaking pre-orders and launch sales of its iPhone 4S in the last few weeks, plus (at least) 25 million installations of iOS 5, its latest and greatest version of its mobile operating system. Those sales will definitely bring a lot of app sales with them, considering that the iPhone is now available for three major U.S. carriers for the first time.

Android’s no slouch, though, with Google and Samsung unveiling the Galaxy Nexus smartphone last week along with Android 4.0 Ice Cream Sandwich, which promises a whole lot of improvements. While Google is ahead in app sales now, Apple might be able to make a fight of it. But in the end, the sheer size of Android coupled with continued improvements should solidify Google’s platform as the top app-selling platform.

That’s the prediction, anyway. Ice Cream Sandwich has a lot of promise, but Apple has been slugging away at this mobile-and-tablet game for some time now. Undoubtedly it has some tricks up its sleeve. Google will have to continue to offer lots of value and innovative features with Android to stay on top, now that it doesn’t have a monopoly on most carriers in the U.S.