I wouldn't suggest for a moment that we should stop pushing for better models. I can't imagine that anyone would thing that we should just say "that's good enough" and accept the errors. My point is that any critisism has to be constructive. We can't yell at the manufacturers and say their models are disasters and expect them to listen. Any dialogue has to be reasoned and constructive. The reason for this is the lack of competition in the industry and the fact that even the people complaining about the models are still buying them (with a very few exceptions like your 20k customer). If one of them makes a gaff on the pre-production model which is pointed-out, they will weigh up potential lost sales against the costs of repeating part of the pre-production cycle. I'd suggst that in many cases, the costs would be such that they'd just live with it. I'd guess that's what happened with the 50 windows. The lack of droop was pointed out quite some time ago, but not corrected.
I'm surprised that your customer thinks that "one of the manufacturers" has lost the plot. Have any of the big three actually made a retrograde step in the last couple of years? There can be little doubt that the mechanisms have improved in recent times, as has the level of detail. Perhaps the extra detail just opens up the potential for more errors!!!
Adrian