I believe what it's referring to is that post 5.6.0 the perl library directory (say /usr/lib/perl on a typical install) installs into a version-specific subdirectory (so you'd see /usr/lib/perl/5.8.0, /usr/lib/perl/5.8.1, etc.). However ancillary utilities such as perldoc would all overwrite the same /usr/bin/perldoc.