No, John that is not necessarily correct. Again, you need to research the this so that you have a better understanding.
I don't have a copy of my masters thesis handy but I do recall that there is a compromise between HC/ CO and NOx (NO and NO2) levels; that compromise is operating at stochiometric fuel/ air ratio. You could operate lean to improve fuel economy but this will worsen NOx production. So, we burn a little more fuel to ensure efficient operation of the three way catalytic convertor.
