You need to remember that these customer service people have very little technical support - and are as likely to be quoting back things they read here as anything else. Yes, maybe the metal back doesn't help - but the problems people are having seem more go/no go than just bad signals.
We already know that most of the people on this thread are not inclined to be very technical in their investigations - trying to stir up press at this point is unlikely to be productive.
My SGS 2 has really poor GPS performance some of the time - it seems to have a state where it doesn't ever lock (just flashes up a few says detected then drops them), so software issues are perfectly possible - as are simple things like the antenna being incorrectly connected. You don't think they ever tested the GPS performance in the final caseworks?
HTC M8, SGS3 (nearly dead eMMC), TF201, Nook touch