Official Google Blog: The meaning of open
http://googleblog.blogspot.com/2009/12/meaning-of-open.html

As Google product managers, you are building something that will outlast all of us, and none of us can imagine all the ways Google will grow and touch people's lives. In that way, we are like our colleague Vint Cerf, who didn't know exactly how many networks would want to be part of this "Internet" so he set the default to open. Vint certainly got it right. I believe we will too.

Google Manifesto