But people who are not having a problem are much less likely to go to the trouble of proving things are fine - human nature. Having said that, just because noone has posted the video evidence as requested also does not prove anything.
In general, the overwhelming majority of those lucky enough to have secured the iPhone 4 for launch couldn't care less about the reception issue.
However, on this forum, and given the spirited defense of those who don't have a "defective" iPhone, I'd imagine there are plenty who would make an effort to disprove the OP's hypothesis.
It only takes one exception to refute his entire hypothesis. Just from reading this forum, there appears to be a plethora of people whose phones are "fine," but others in relative proximity aren't.
For instance, your phone is fine in your apartment, but your buddy's isn't at his house 20 miles away. Bring your "non-defective" phone to his house and test both simultaneously to see if there is erosion on both. If you run this test, and yours is fine, while his signal is eroding, then it is a defect on his phone. However, if the otherwise perfect phone in your apartment exhibits the signal erosion, than it isn't a defect, but an inherently inefficient antenna design, relative to other phones that do not exhibit the severity of signal erosion when held in a similar fashion at a given geographical location.