I wonder if the bandwidth even costs Google anything any more. Certainly they have peering agreements with any large ISP already. And they need some sort of egress to balance all the data collection they're doing from a bazillion Android devices and Chrome instances.
Not only peering agreements but 70%-90% [0] is directly served from your ISPs data center. google sends your ISP the server but rackspace, power and network is provided by the ISP.