Following yesterday’s Flurry report that the last week of 2011 was the first time that the total amount of apps for iOS and Android devices crossed the 1 billion downloads milestone, Distimo has compiled data that shows the Google Android market has crossed milestone of 400,000 active applications throughout the world.

Distimo cites free apps as the leading cause for Android Marketplace reaching the 400K mark as 68% of all apps downloaded on Android devices was free content. As we’ve mentioned before, free apps, otherwise known as the freemium apps, are becoming the emerging business model in app development. The model has boosted the downloads from the Android Market nearly 166% since the beginning of 2011.

Distimo drew up a timeline comparison of Android’s ascent to 400K downloads with Apple’s trajectory to the same milestone. While Apple’s climb has been relatively steady to each subsequent thousand-download marker, Android Marketplace actually took longer to reach the 200K and 300K marks than Apple App Store. However, Android Marketplace took considerably less time to expand from 300K to 400K than Apple App Store, which gives cause to speculation of whether Android will be able to maintain this steep increase as it approaches future milestones.

One reason Distimo offers for the boom in Android app downloads is the application store’s 100,000 active developers publishing on average 4.1 apps a piece. More apps developed make for more apps downloaded, for sure. At any rate, Android Marketplace appears to be on track to outpace Apple App Store in 2012.