The BMWs also use a urea based system that separates the NOx into Nitrogen and Oxygen and does it very well. However, those systems are expensive and add a lot

The BMWs also use a urea based system that separates the NOx into Nitrogen and Oxygen and does it very well. However, those systems are expensive and add a lot of costs to the car. VW wouldn't be able to sell their TDI cars as cheaply if they had to incur this cost. That's why they pass and why they have passed alternative tests. I just bought a new GTI about a month ago...not sure if their gas cars will take a valuation hit or not due to VWs reputation hit. At least it wasn't a TDI Golf or I'd be extremely pissed.