Once again, the "hype" and knowledge of the Nexus is mostly limited to tech boards and tech fanboys. There are not huge numbers of people delaying upgrades waiting on this phone. It isn't going to "crush" the RAZR or Rezound or any other phone at VZW because to most people walking in the door it will be just another high-end phone with comparable specs. Truth be told, the 32gigs of storage might turn people off, because it's one of a few specs people understand and compare (right or wrong, $300 for 32gigs loses vs. $300 for 48gigs). I also think Moto is a much bigger brand name in the states for people off the street and for people who actually still use their phone to, you know, make calls.
That said, there may be something to VZW's holiday return window. While many people are oblivious to the pending release of the Nexus, when people start seeing it in the wild, with its ICS goodness, more than a few might contemplate returns. That's a number that is perhaps not insignificant, and a release later in December will help minimize that.