The majority of people who buy an iPhone would not return it for an Android phone. The majority of those wanting an Android phone would not buy an iPhone to begin with. The fact that the Razr goes on pre-order tomorrow has no bearing on the iPhone.
However, those who buy a Razr might very well return it for a Nexus because it is the same platform. If you don't think that Verizon would push back the release of a non-Droid branded phone past the 2 week return date cutoff for a Droid branded phone, then you are naive.
It is my opinion that this is the exact reason Verizon has been so hush hush about the release date of the Nexus. If people know the release date of the Nexus and Verizon starts publicizing it officially, then people would probably hold off on buying the Razr. Believe it or not, there are people that do not know about the Nexus. They do not follow Android closely and only know about phones when the carriers officially announce them and start marketing them with posters, putting them up on the website, etc. People already know about the Razr. There are ads, it's on the site, etc. There's absolutely no mention of the Nexus anywhere regarding Verizon. All makes sense to me, especially considering how close my source is to the Droid marketing campaign.