@cleeds is absolutely correct. The power generation Hertz (cycles per second) is very tightly controlled. It used to be that electric clocks were among the most accurate, given by law a day had to have a precise number of cycles. No longer the case I believe.
Still, cleeds is right BUT, eliminating anything not 60 Hertz is a good goal in eliminating noise and distortion that may appear long after the power company generates it.