On my car there is a separate switch on the throttle body that tells the ecu when the throttle is fully closed. The switch is used only for coasting fuel cut.
I'd imagine other cars are using something similar. The fuel cut couldn't be dependant on the vehicle slowing down, otherwise you'd stall everytime you went uphill.
What about stepping on the brake and gas at the same time? Does it cut fuel on your car?
When I hit the brake/gas pedals at the same time, the engine revs up and overcomes the brake (like the drifters do!!!!). The PCM must have a rock-paper-scissors rule where the brake state is ignored if the user presses the gas pedal. Gas beats brakes.