satya - Saturday, April 18, 2009 11:10:09 AM

Here is what the google docs say about it

We've also made changes to the developer tools and the structure of the SDK itself. Future Android SDK releases will include multiple versions of the Android platform. For example, this early-look includes Android platform versions 1.1 and 1.5. One benefit of this change is that developers can target different Android platform versions from within a single SDK installation. Another is that it enables developers to install Android SDK add-ons to access extended functionality that might be provided by OEMs, carriers, or other providers. We at Google are using this feature ourselves: this early-look SDK includes an add-on for the Google APIs. This add-on provides support for the Google Maps API, which was previously embedded in the "core" SDK.