Because there are two separate issues.
1.) If you put your hand near ANY cellphone antenna, the capacitive effect of your hand detunes the antenna to some degree. As you put more of your body closer to the antenna, the effect increases, detuning it further. So, for example, holding it in the right way in either hand may cause it to drop a bar, maybe two. Putting both hands around it and squeezeing it tightly might cause a drop of 2 or more. It depends on how close the antenna is to the body of the phone, how strong the effect is from your body and how tightly you're holding it. If this doesn't happen to you it's most likely because you are in an area with decent reception or the capacitive effect of your hand isn't enough to affect the phone.
2.) The iPhone 4 and ONLY the iPhone 4 has a gap in the band around the phone to separate the band into workable antennas. Bridging the gap in the lower left of the antenna will, if you're in an area of less than perfect reception, cause the signal to drop to or near zero and any call or data transfer to drop. If you bridge it with something that's semi-conductive, like a finger or your hand, the drop may be anywhere between a couple bars and no signal at all. If you bridge it with something conductive, like a wire, it can immediately drop to zero.
I listened to what Jobs said and saw what was up in the background and it doesn't make sense. He talks about the first one and shows pictures of the second as if they're the same thing, but they're not. I can't believe Apple doesn't know the difference so I'm assuming we're getting snowed so Apple can avoid a huge, costly, image ruining recall.
