What is the IUPAC systematic name for methane?
The latest edition of the Blue Book, the 2013 Revision, clarifies this:


  Methane is a retained name (see P-12.3) that is preferred to the systematic name ‘carbane’, a name never recommended to replace methane, but used to derive the names ‘carbene’ and carbyne for the radicals $\ce{H2C^2-}$ and $\ce{HC^3-}$, respectively.


So it seems to be the case that the systematic IUPAC name is only there for consistency with the ions, and is not recommended (and not used) to describe methane. Similarly, "ethane", "propane", and "butane" are preferred to their systematic equivalents "dicarbane", "tricarbane", and "tetracarbane".