> In reality, our 5-volt CMOS system will consider anything above 1.67 volts to be a 1, and anything below 1.67 to be 0.

Worth noting that the region from 1.67 V to 3.33 V is undefined and systems in practice will not behave nicely for signals in this range. A CMOS logic 1 needs to be above 2/3 Vdd to be reliably recognized.