Apart from a few reports on so called tech blogs and websites I have not seen any irrefutable evidence that it is either a hardware or software problem. Hence I suggest we wait for an official response before we all go stir crazy.
You haven't looked in the right place, it's really just antenna theory and math. Any ham radio operator will tell you that any given frequency has an optimal antenna length. In vacuum, if I recall correctly the formula is L=300/f where L is length in meters, f is frequency in MHz. If it's too long or too short, reception falls off and power from the transmitter is reflected back to the transmitter in the form of standing waves. The ratio of power sent to power reflected is the Standing Wave Ratio or SWR. The worse the mismatch of the antenna to the operating frequency, the higher the SWR until it reaches, for practical intents and purposes, infinity where all the sent power is reflected back and, conversely, there's no reception at all. If the power is high enough and components sensitive enough, you can burn out the transmitter with a mismatched antenna.
Now, the operating frequency of a cellphone is pretty high and a half wave dipole, for example, is measured in centimeters (this being opposed to, say, AM radio frequencies which are low and their antenna lengths are measured in 10s or 100s of meters). When you bridge that gap in the band, you just added a long stretch of metal to the antenna, given the operating frequency, which detunes it to where there's almost no reception and the SWR goes through the roof. You can "death grip" it or lay it on a table an bridge it with a wire, not even touching it with your hand, the effect is the same. Further, obviously your hand conducts electricity or it wouldn't be possible to be electrocuted. Therefore, your hand bridges the gap and the antenna is detuned.
I'm hardly going "stir crazy" about it, I simply think Apple needs to own up and properly fix the phones. They aren't cheap, they come with an expensive 2 year contract and all Apple needs to do is replace the metal band with an identical metal band coated with some non-conducting material that won't easily flake or chip. It's that simple. A better way would be to replace it with a hollow, plastic band and, inside that, use insulated copper strips as the antennas. That would allow for an external antenna for superior reception while protecting the antennas and keeping the capacitive effect of the hand at a minimum. The reason I keep posting this is because there are three issues and people confuse them or flat out lie, if they're not too busy acting like a 6 year old throwing a tantrum, that is. But it's nothing more than antenna theory and math that's been around for a long, long time.
One other thing I've pointed out elsewhere is that there are actually three different issues at play:
1. What I described above. This is the one Apple denies because it's a potentially very expensive hardware problem and the reason Consumer Reports gave the phone a failing grade. Unless you have perfect reception to start with, if you bridge the gap in the band, the cell signals disappear entirely.
2. Almost any cellphone can be detuned to some degree by the capacitive effect of your hand. I assume this is the "death grip" everyone posts about but it's NOT the same as #1. Usually cellphone antennas are already so poor this effect doesn't make a lot of difference. It might cause the phone to drop a couple bars but unless reception was poor to start with, you don't drop calls.
3. Apple's magic formula it uses for displaying reception bars on the screen. It doesn't make any sense to me, previous iPhones show better reception when, in fact, they're worse than the iPhone 4. I figure Apple just kind of made this one up in hopes customers accepted it as an excuse for #1 which, obviously, failed miserably. It also won't effect where, when or how you use your phone in any way.
If you can't believe someone with almost 40 years of experience designing and using antennas, find a testing lab or an amateur radio operator of at least General class (they have to know this stuff to pass the tests required to obtain their license), take the cellphone with you and ask someone to show you what I just explained. If they have any decent test equipment, especially an o-scope, it's simple.
