It's neither of those. Lots of people here have the same symptoms, to the point where it's considered pretty normal for a Phaeton. I usually run with 50/46 to try to reduce it, but it doesn't help much. They also suffer from cupping.
I purchased a tread depth gauge and plan on taking measurements every 500 miles. Come hell or high water, I will find out why I've gone through tires so quickly. I will be upset, to say the least, if I find out ball joints are to blame. I've visited three differ shops and all have given my suspension a clean bill of health. Should it be expected that they would unload the suspension to check the ball joints?
I wondered about ride height too. Especially after lowering to Euro spec height (2004's only). With such a well engineered car, why would they not take the options for different ride height into consideration?
I know so little about suspension engineering/design, but I recall reading an excerpt on specific suspension designs that can handle slight ride height modifications without the need for alignments. I can only assume VW took this approach with the Phaeton. If not, this is a design fail on their part. If not for the original and North American ride height, at least for the difference in ride height when reaching highway speeds.