Comment by Zigurd

In fact, Google was concerned about Microsoft more-strongly binding Windows Mobile (Windows Phone came later) to their Web ecosystem. Microsoft was working on Windows Live Search, which would later be replaced by Bing.

At the time, Windows Mobile was the epitome of a modern mobile OS. It had a real(ish) browser and a VM-based app runtime for a modern (C#) language (albeit optional and not nearly as tightly integrated with OS middleware as in Android). Google saw that an ecosystem such as Windows Live is much more critical to a mobile device than it is to a desktop PC. The nature of Android more closely reflects the threat from Microsoft than from iPhone.