I am sure Google has so many data centers in whole world and best for searching data but they would need many data centers to run their operations they are after world domination....
Google has a very robust and redundant architecture and their server clustering allows them to serve requests from the nearest Datacenter.
Thus improving response time.
While I was reading on Google's architecture I found the below video very interesting as it provides a visual to their infrastructure
Google has the most largest numbers of data centers all over the world and nobody knows the exact number of data centers they have. According to what I have searched, they are secretive about their data centers because Google believe its data center operations give it a competitive advantage, and says as little as possible about these facilities.