Also there are many different versions of this survey, a quick search on Goggles showed me Auto Express, What Car and Autocar have their own versions. Top Gear too. Plus then the US ones. So to get a true picture is difficult.
Plus of course, it all depends how many owners actually took part. As you rightly say, 'prestige' mark owners are far more likely to share their opinions. There is nothing to say that each manufacturer had the same number of models surveyed, which would automatically scew the percentages. Buy that works both ways too of course. I mean look at Alfa Romeo, right down at the bottom but they only make two models!
And let's not forget, 99% of Chevrolets are rebadged Daewoos...
Sepang Blue 8V RS3. Loud Exhaust. Loud Music. Louder Interior. Quiet Exterior.