apt-cache search nvu returned nothing, although I could still find the package by searching packages at debian.org
More investigation turned up this.
Final upshot is that nvu was pulled from the Archives yesterday due to abandonment upstream. I'm not quite sure what that means, but there is certainly no sign of abandonment at the Nvu home page.
If this is a result of some disgruntled Debian Package maintainer's snit, it's a step too far over the line.