"Calls to unify the nation's power network under a single frequency remain strong. But doing so would require a major infrastructure overhaul, including facility upgrades and land purchases- that would cost up to tens of trillions of yen, according to experts."

http://www.yomiuri.co.jp/dy/national/20110424dy02.htm

The split between 50Hz (eastern Japan) and 60 Hz (western) dates back to before 1912; the old ancestor of Tepco chose the German 50Hz and the ancestor of Kansai chose U. S. 60Hz.