The slick iPod metal case is an example of style in direct conflict with substance, with style winning.

I just got off the phone with tech support. Many third-party headphones have jacks have a plug that widens at the base, shorting audio ground to the case. This is NOT supported, and will cause static and distortion.

Easily fixed by insulating the case or plug, but an ugly fix that requires maintenance.

They don't see this as a recall issue. It is an obvious design decision going in, they are very smart people, they made this call very intentionally. I can picture the conversation.

When people build their own headphone amps, they pay extremely close attention to case ground, and separating audio ground. Google for "virtual ground"...