Oh, Neat!
Ok, so it seems like earlier models used either a modulating gas valve or multiple heating elements which maintained a relatively even exhaust temperature. While latter models switched on their bias heater for low heat 10-15 minutes before the cool down.
Neat.
My Maytag Centennial dryer does this, it will switch on low heat before the cool down. The concept doesn't work well with heavy loads, though it is what it is.