I just replaced my throttle cable today and had a friend verify throttle plate position while I put the pedal to the floor. At WOT, the plates were at 90 degrees. No hyper-extension beyond horizontal.
The 2 plates are activated in sequence to ensure a bit more lower end for part-throttle applications. If we were to replace the 2-plate throttle body with a single plate that equaled the total area of the two plates combined, you'd have a pretty crappy low end/off-idle response. It's actually a pretty clever set-up.
The throttle lever has 2 places where you can fit a throttle cable. One is for the gas pedal, and the other is for the cruise control cable. Most of our cars don't have cruise control. The throttle cable goes through the holes closer to the firewall.