I used to work as an engineer in the auto industry, at a major parts design company which worked with virtually every manufacturer, and you couldn't be more wrong. Cars are better than they've ever been, and there are plenty of data to support that fact. Almost every car built today, barring only a handful of individual lemons, will exceed 250k mi on the original engine without a rebuild with normal maintenance--a rarity for the all metal cars of yesteryear. And that maintenance is less and less year over year with 10k+ mi oil changes now standard, going on up to 30k in many models.
Modern plastics are cheaper, but they're also lighter, chemical and corrosion resistant, non-conductive, and often tougher; there are so many more options for plastics these days than there used to be, and tooling costs have dropped dramatically with the adoption of CNC, so it's no wonder these materials are more and more widely used. Wiring gauges have decreased--so what? Why carry around more weight than you need? Modern digital electronics mean less power is being transmitted to individual devices, and modern systems are operating at higher voltages, both of which mean lower current which means more safety with smaller gauge wiring.
Automakers, even the American ones, most definitely do care how long cars lasts and don't intentionally design them to fail on the second owner or after the warranty period. All manufacturers design parts with intended lives well beyond the warranty period; but you can't design for forever. Enhanced component life costs you money and saps performance. So there's a balance, but car manufacturers know they're in this game for the long haul, more than just about any other industry I've been involved with, and they know that when someone's suffers a catastrophic failure after six years, that informs not only their next purchasing decision, but that of all their friends and family. American companies see 20 year old Honda Civics driving around now and *know* that's powerful advertising for Hondas sold today. Everyone in the industry wants to be last generation's Honda. JD Power may not be the most scientific survey, but it's absolutely no surprise that the industry has converged to a high standard of quality.
Lastly, to address some other points people made about the death of the shadetree mechanic; I can't believe that the /. crowd of all people would fall for that tired line. Scantools are cheap, USB interfaces are cheaper, and the manufacturer specific protocols have been reverse engineered in many cases. For most vehicles it should be an easy exercise for a hacker to get his laptop up and running on the CAN bus and start talking to every component in the car. In most cases the car will simply tell you what's wrong ("Help, my mass air flow sensor is bad!") and you just have to replace it, without needing a whole parts shop to try and replace until things start running right. Fuel injection, in particular, is so much easier to deal with than carburation. In the long term, I think cars will start to adopt Health and Usage Monitoring Systems (HUMS), like many aircraft now have, so that they'll be able to tell you "I think that CV joint is going bad, maybe you should grease and reboot it" before it starts making noise and needs to be replaced.