Is it true that each and every signal has multiple frequency components?
The only signal, that really has just one frequency component, is an infinite sine signal. Limiting the signal duration in any way is bound to produce other frequency components, as time limiting can be thought of as multiplying with a rectangle window, which translates to convolution with an si-function in the frequency domain, thus introducing new frequency components, however infinitesimal.

As for your example: the 60Hz AC power "signal" is messed up with all kinds of stuff coming from devices connected to the grid, that "backfire" into it. Also, the 60Hz are not really constant, they vary ever so slightly around 60Hz.