I have a theory on how these issues slipped by. I think all of the folks who had units to beta test had bumpers on them so casual observers couldn’t tell it was the new phone. The bumper would certainly mask the antenna issue because it would insulate your hand from the metal. I wonder also if the design of the bumpers wouldn’t also mask the proximity sensor issue causing dropped calls. The sensor works on light so a bumper may seal against your skin and block light whereas a naked phone would not.
Everyone I know with the iPhone 4 has all of the reported problems. Most have gotten bumpers and the problems go away.
The bumpers cost WAY too much for what you get. I am sure they would cost Apple next to nothing. Why doesn’t Apple throw the bumpers in and be done with it?