Check out Kirk Allen Evan's blog entry (http://blogs.msdn.com/kaevans/archive/2006/06/11/626299.aspx) . All through it, his reasons given point to calling it something less than .Net 3.0 IMHO.
Again, note that .NET Framework 3.0 is an additive release to .NET Framework 2.0. With .NET Framework 3.0, the languages still use the 2.0 compilers, and leverage the 2.0.50727 Framework.It is based on 2.0 for everything so why not keep with that!!! The version number really doesn't make anything clear!