I think it's QC, not R&D. An Apple store recently opened near me so I got to play with some iPhone4's for a while in the store, and I might go back because I found some interesting things. Two iPhone4's right next to each other, one dropped to 0 bars in the store within 30 seconds of merely touching the antenna gap, the other one dropped 2 bars after a couple minutes of death gripping it. There was NO discernable exterior difference in the phones. I even scratched at the metal to try to see any noticeable polyvinyl coating on one v the other. At that point, the third "Genius" in a matter of 90 seconds asked if I needed any help, so I began to feel awkward poking at the phone (it was very busy in the store).
I would not be surprised if one manufacturing plant in China has a poor Quality Control or Quality Assurance division that just is not doing their job. I've seen pictures of iPhones with reversed volume controls on the side, and this lends to that explanation, and to Apple's personal assurances that they've thoroughly tested these phones. A coating of some sort should be sufficient to abrogate any conductivity, and it does not make sense that Apple did not think of that. I might return and take a look at the batch numbers on the back of the iPhones I played with in the store. I'm still not buying one, because I have no idea if I'm going to get one that works or one that does not, and I'm not playing games with the return people. By the time they get it sorted out, if ever, the Next Big Thing will probably be out. I still own the original iPhone, because nothing has seemed worth the upgrade yet.