Population in the US: 313.9 million (2012)

Population in Europe: 739.2 million (2011)

Population in Japan: 127.8 million (2011)

Number of servers for NA+EU: 20
Number of LEGACY servers for NA+EU: 5
Number of server for JP: 20
Number of LEGACY servers for JP: 5

so this is a disproportion between population and the number of servers.