Well the sad thing is, for most people the JD surveys are the way they form an opinion on many new cars and trucks. I was watching the news last-night (before the UK/US bombing scare) and they were talking about the ratings and how great Lexus is... Great, its a good thing these people have no idea what they are talking about.
All it does is create bragging rights for the given brands, and thats about it. It does point out that the American brands can do as well as those from Japan, and how many European brands are a bit overrated in quality, but nothing more. There is still the car-by-car baisis in which one Jetta might to better than the one made right after it, one Camry may have more issues with it's transmission while another may have some serious quality issues with the interior.
It does make you wonder who exactly spends all of their time complaining for JD power to get these scores together. First time buyers? Long-time drivers?
Take the Volkswagen scores. I don't know many people who just wonder around and suddenly decide to drive a Vee-Dub, it is a pretty well established brand with a well-established fan base. Of course VW is trying to change it, but most VW owners are well aware of the quality issues, and for the most part, don't complain about it as often as other owners would.