While the signal strength comparisons and anecdotal reports are interesting, They're no substitute for a controlled environment such as the detailed tests performed for submission to the FCC for approval. Among other things, those tests measure antenna gain for a given frequency, and you can compare that to other phone models.
Lots of things can affect the strength of the signal, including other nearby RF sources. Some phones may be better at rejecting interference. (Comparing two different phones side-by-side might cause interference that affects one phone more than the other.) Also, the signal strength can fluctuate just due to varying atmospheric conditions, time of day, distance to the tower, etc. If you're in a good reception area, you probably wouldn't notice any significant problem.
Since this topic seems to be getting press attention and if enough people report the issue, Apple will need to address it. If anyone knows what the issue is it would be Apple's engineers. Hopefully, they didn't know there was a problem and the phones were released anyway because form took precedence over function.