> Plunkett realized that he could replace this pricey switch with a potentiometer -- essentially an adjustable knob that divided voltages and acts as a variable resistor -- and achieve the same effect. “The switches were very expensive -- about $4 each,” Plunkett continues. “The potentiometer would only cost about 30 cents.”

Maybe he's talking about a rotary switch coupled to numerous external components? Such a thing has tonal virtues: you can switch paths that have different L, C and R values.

But, no; it's just described a simple switch:

> This switch, invented by British engineer Dick Denney and installed on all Vox AC-100 amps at the time, stood for “middle range boost.” When flicked on, it would highlight the middle sound frequencies of the guitar (notes between 300 and 5,000 hertz); in doing so, it would tame the extremes (very high and very low pitches), and produce a flattened, smoother sound.

It seems like nonsense that some at most DPDT switch would cost $4 versus a potentiometer at $0.30. Not for equal quality.

Maybe someone can shed some light on this?