Just like the sysadmin is responsible for patching the system. With Red Hat's Satellite Server, apt-get, etc. having two different Perl's is not that difficult. The reason you think it is is because you are thinking of a scenario where you have to manually install the second Perl. The point is that the vendor/distro has to support multiple Perls, which is much easier (more QA, less people duplicating work, etc.). This very thread shows why it is better to have two. What is a bad idea is having OS scripts, third party vendor scripts, etc. relying on the same Perl that people are making changes to.