One way to look at Google vs. Facebook European data center locations is to plot on a map the sites.
A - Google Dublin
B- Google Hamina, Finland
C - Google Belgium
D - Facebook Lulea, Sweden
Google has three major data center sites. In Asia, Google has three future sites - Singapore, Hong Kong, and Taiwan. Recognize a pattern? Three is a good number, says GreenM3 :-)
Keep in mind given Google has built its three data centers it most likely looked at sites all over Europe before it picked its three locations. Think about being in three sites as an option to building one mega site. I watched an established company follow the advice of the so called data center experts justifying a single site as their first data center. For less than 10 MW, it can make a lot of sense to have three 3 1/3 MW sites to enable geo redundancy of services.