Re: In reality...
The NOx problem is caused by running the engines very hot (improves fuel economy)
The NOx is allegedly countered by urea injection (except in VWs).
However, if you think anyone can compute the exact amount of Urea to inject in a 16 litre truck engine which can go from idle to max RPM and from cold to hot, each time it changes through its 24 gears in climbing from 0 to 56MPH and back between roundabouts and traffic lights, then you are going to need some seriously magical thermodynamics and sensors as well as computational skills.
The fact is, the Urea injection lobby (read people funded by the Urea sellers) are the problem here, not VW,