Interesting post! Many clocks (analog and digital) use a quarts crystal and a battery. However it is cheap to use the AC utility frequency, especially in things like coffee pots and ovens that have temperature changes that would create error for the quartz.

I have read the power company will schedule frequency offsets to compensate for corrections of error. In other words if the frequency is low enough to loose time, then the utility provider will schedule increases to synchronize time.

Your post got me wondering if the power company was motivated to correct for time, as mentioned above. This site has some interesting info, as did wikipedia

--3D