An official Google spokesman said, "A thriving developer community is an important part of creating a better mobile experience for users around the world.. We hope that offering devices to developers will make it easier for them to create and test great applications. This is inline with other efforts to support developers which also includes our Android Developer Labs World Tour and our upcoming participation in the Game Developers Conference."
If you want to read a copy of what Google sent out to those developers who will get a free phone, check out the source link.
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source: Google via AndroidandMe