I went down to my local apple store and tested out 9 iPhone 4s. Of those 9, 4 showed the problem, while 5 were perfectly fine. The test was to place my thumb on the lower left spot, thus "shorting" the two antennas. I repeated my test on each one multiple times and it was consistent. This leads me to believe it's a production batch issue and not any of the other theories being floated around.
Any software fix will only be covering up the problem.
Of course, who doesn't use a case though?