I just today listened to the BBC Bottom Line Special [1] on this, and their guests, one who used to run Jaguar, and an expert on VW, don't buy it. Their argument is that the engineers in VW could have done a proper job, but the technology would add another $500 to each vehicle, and VW must have been looking for a way not to spend the $500. And all the other VW engineers would ask "How did you do it?".

[1] http://www.bbc.co.uk/programmes/b06jt518 9mins 15 onward