On Windows, you could always (or at least since Perl 5.6.1) take the Perl directory and move it wherever you like. You only need to update CPAN/Config.pm, but Perl.exe would still find all relevant directories, like lib/ and site/lib, as long as Perl.exe resides in bin. On older operating systems, especially the Unixish variant, all the directory paths are hardcoded in the perl executable, and thus you will encounter various problems should you move the Perl libraries from (say) /opt/perl/ to /usr/local/perl/ without recompiling or patching your perl executable.

I'm happy that Nick works on bringing Unixish systems up to par with Win32-based systems!