My advice would be that your wonderment about giving your local store "s#*t!" would be misdirected and ignorant.
Not sure I can tell you why all people are replacing their phones but some are trying to get a guarantee that an insurance replacement would net them a GSM phone which gives them a cheap/backdoor way to upgrade their current service.
As of this moment, there is still no new, verified information that I have seen which states CDMA will stop working any time soon. Since the merger, my crappy 1.5 x 1.5 market (Philly) has seen some growth and I hope it continues to get better. A lot of coverage deals with where you live. If you were to follow in the foot steps of someone in a completely different coverage area you could end up with a different outcome.
Metro and Tmobile announced that they would be combining their LTE networks and from what I have read and seen in the past week, it has already been done in TX. The person posting their speedtest was using an LG Motion.