I wouldn't be a bit surprised if this is a major part of getting this phone ready for release. Only the people that are part the VZW testing program know for sure.
I am a member of the test team for a Satellite TV provider and we download new software each week. We submit reports via our receivers (through a broadband connection) when we find issues. Fixes are implemented each week until the software is deemed suitable for general release. Sometimes the process just takes awhile.
My guess is that an issue was identified with the radio which made the phone unsuitable for release. Probably among other things that needed to be tweaked. The fact that VZW is being super cautious regarding the release of this phone is no surprise. They know that the early adopters of the GN will be techies who will push this phone to it's limits. Although some refuse to give VZW any credit for anything and would rather throw internet tantrums than use logic and reason, I am happy that VZW is taking it's time to ensure that this phone is ready for release.