This may be one of those times when the rumor mill had the story right...
There was a story on one of the Android websites when the Nexus S was delayed (after the leak of the Best Buy ad mockup, etc). The story was that Samsung testers determined the phone needed a dual-core CPU, and thus plopped one in the Nexus S.
The problem, though, was that Gingerbread wasn't optimized for dual-core processors. This seems strange, since it has been a given that dual-core CPUs were arriving Q1 of 2011.
Still, this would explain the delay in bringing the software out, especially a delay which seems very last-second, based upon the Kremlinology of the arrival of the statue, etc. Both the Nexus S and Gingerbread could see their arrival before Christmas, but this is something which will simply happen on its own schedule.
Meanwhile, Google needs to get Gingerbread out into the marketplace so it can bring Honeycomb out shortly thereafter. Honeycomb is the OS built for tablets, and given the heat in that sector of the market it makes sense that Google and the manufacturers want Honeycomb out ASAP.