In an ArsTechnica article, by Ron Amadeo outlines Android's history, focusing on how Google is slowly locking down the platform.
Originally designed as an open source project to combat, what was perceived to be, the inevitable dominance of the iPhone (and Apple) in the mobile space, Android no longer resembles its previous self. Because Android is technically an open source project (though many disagree) it doesn't necessarily mean the platform's huge market-share accurately represents a clear "win" for Google.
As we've seen with the struggles of Windows Phone and Blackberry 10, app selection is everything in the mobile market, and Android's massive install base means it has a ton of apps. If a company forks Android, the OS will already be compatible with millions of apps; a company just needs to build its own app store and get everything uploaded. In theory, you'd have a non-Google OS with a ton of apps, virtually overnight. If a company other than Google can come up with a way to make Android better than it is now, it would be able to build a serious competitor and possibly threaten Google's smartphone dominance. This is the biggest danger to Google's current position: a successful, alternative Android distribution.
While Google's apps are present on the majority of high end Android phones - including Samsung and HTC - the biggest challenger by far has been Amazon. They have deliberately taken the AOSP and opted out of Google's Handset Alliance, taking Android (re-branding it Fire OS) in their own direction.
But Amadeo argues that Google has been slowly closing down Android with each iteration.
There have always been closed source Google apps. Originally, the group consisted mostly of clients for Google's online services, like Gmail, Maps, Talk, and YouTube. When Android had no market share, Google was comfortable keeping just these apps and building the rest of Android as an open source project. Since Android has become a mobile powerhouse though, Google has decided it needs more control over the public source code.
For some of these apps, there might still be an AOSP equivalent, but as soon as the proprietary version was launched, all work on the AOSP version was stopped. Less open source code means more work for Google's competitors. While you can't kill an open source app, you can turn it into abandonware by moving all continuing development to a closed source model. Just about any time Google rebrands an app or releases a new piece of Android onto the Play Store, it's a sign that the source has been closed and the AOSP version is dead.
He uses Google Voice Search as an example. Android AOSP's Google search hasn't changed since the days of Froyo (Android 2.2), and it can only conduct web searches. In contrast, Google's latest version of Android (4.3 and soon to be 4.4) has Google Now - an amazing personal digital assistant with voice recognition, a card interface, and very accurate and relevant predictions and suggestions.