I imagine most modern cars use a fly-by-wire throttle in order to manage exhaust emissions and modern driver aids. The accelerator position sensor does not go to the throttle, it goes to the engine management unit. It is the emu that decides how much to open the throttle and it makes the decision based on various inputs, not just the accelerator position. So, what are the other inputs? Engine temperature, engine revs, sensors in the air intake and sensors in the exhaust. On my car the EMU also regulates the throttle to provide traction control and stability control.
But, to answer your question, the Mazda RX8 does indeed have a fly-by-wire throttle.