the stage tarballs and the binary packages are using the same suffix but are not files of the *same* structure. my suggestion is that a suffix should only be used for exactly one structure. the structures differ as untaring shows by commenting the trailing garbage. my suggestion: using tar.bz2 for the *real* tarballs like the stageX files.
I just was reminded of this thing again: I use bash_completion a lot and wanted to unpack a stage3 tarball. bash_completion will not expand tbz2 filenames on hitting tab which is ok in my eyes. Please think about renaming the stage tarballs to tar.bz2...
OK, on the to-do list for the 1.4_rc1 release :)