So you are saying that the volume of cars is the reason why VW did so poorly in the JD Powers quality survey?
I'm saying it's a big contributing factor, yes, but there's a whole gamut of issues that make quality surveys less than scientific. Some brands attract more nit-picky people than others, which would influence the answers they're likely to supply in a survey. People are swayed by their preconceptions, by patriotic notions and by who-knows-what else. Case in point: in the US JD Powers survey 3rd place overall went to... *drumroll*...
Cadillac 
Now, I don't know about yours, but in my world there is no way that a Cadillac is a higher quality product than an Audi, a VW, a Beemer or dare I say it, a Hyundai. But it is true-blue US of A material, though...
In a local context the CITI Golf was a major contributor to poor CSI results for VW. No matter how highly it's regarded as an iconic, cultural element of SA motoring, as a car it sucks ass, and it has done so for at least 2 decades. Yet 1000s of them sold, and those people's complaints about their leaky, squeaky, rattly POS Citis carry as much weight as the odd complaint over a missed stitch on a Touareg's leather steering wheel.