The best answer that i think would be that google is upto some thing that solves problems for developer and manufacturer Google has never been into manufacturing hardware. They are an ad revenue based company, and they have been looking for ways to bring their advertising model to the mobile phone industry. What better way to do this than to break from the pack and develop your own mobile platform. Also As of this writing Google has stated it has no intentions of releasing hardware of any kind to compete against the Iphone. Instead it is focusing it’s efforts on Android, a new open source platform for mobile phones
All applications are created equal
Android does not differentiate between the phone’s core applications and third-party applications. They can all be built to have equal access to a phone’s capabilities providing users with a broad spectrum of applications and services. With devices built on the Android Platform, users will be able to fully tailor the phone to their interests. They can swap out the phone’s homescreen, the style of the dialer, or any of the applications. They can even instruct their phones to use their favorite photo viewing application to handle the viewing of all photos.
Breaking down application boundaries
Android breaks down the barriers to building new and innovative applications. For example, a developer can combine information from the web with data on an individual’s mobile phone — such as the user’s contacts, calendar, or geographic location — to provide a more relevant user experience. With Android, a developer could build an application that enables users to view the location of their friends and be alerted when they are in the vicinity giving them a chance to connect.