It's not.
This is now being noticed because of the attention that the external antenna has drawn.
yes it is. Again, I have 2 3gs's and 2 4g's. I have a microcell. Standing 3 feet from my microcell, the 4g's go to 0 bars and "searching" if i touch one fingertip to the bottom left seam. No matter how I hold the 3gs's, I never lose more than 1 bar.
There are two different issues here and everyone is pretending they are the same. putting your hand over the antenna will degrade the signal on every phone, it is true. And that is what some people see.
But many of us go from 5 bars to 0 in 15 seconds just by touching one point, apparently due to a lack of coating (manufacturing defect) on the metal antenna. Anyone who says "i can replicate this on my 3gs" is not replicating this problem - they are replicating the "covered antenna" issue.