CrossRoads:
This article goes into depth of the single gate amplifier. Scroll down to page 8.
http://www.ece.ucsb.edu/Faculty/rodwell/Classes/ece2c/labs/Lab_2_2C_2007.pdf
We don't need it biased to operate in the linear region since the tone output is either on or off - hence the amplifiers output can be on or off as well.
I agree.