well, technically speaking, VZW's LTE as it is now doesn't provide "true" 4G speeds either, so it's not much different, they're all 3.5G technically speaking... and at this point in time, it's too late to make hardware changes i imagine, so it's likely to be software related
and my thought is more along the lines of, as company, does AT&T do a better job launching phones than verizon? true, their network is not up to par and i havent really been in touch with their launches lately, but i do know that VZW has really fell short a couple of times already regarding launching new phones... and while this is their first LTE phone, the LTE network has been up and running for quite some time already
I could swear that I read something somewhere that stated the the commission that's in charge of the "G's"

Found it "...Following a detailed evaluation against stringent technical and operational criteria, ITU has determined that “LTE-Advanced” and “WirelessMAN-Advanced” should be accorded the official designation of IMT-Advanced. As the most advanced technologies currently defined for global wireless mobile broadband communications, IMT-Advanced is considered as “4G”, although it is recognized that this term, while undefined, may also be applied to the forerunners of these technologies, LTE and WiMax, and to other evolved 3G technologies providing a substantial level of improvement in performance and capabilities with respect to the initial third generation systems now deployed..."
http://www.itu.int/net/pressoffice/press_releases/2010/48.aspx