You have a point. But standard wisdom seems to be that you'd be even better off installing a separate copy of Perl (probably from source) and using CPAN to customize that rather than messing with the system's Perl (and this is true for any system with package management that ships with a version of Perl, not just Ubuntu). Though, getting by with the system's Perl can certainly be a simple solution that will likely work well enough for a while. Usually, you will eventually get to a point where using the system's Perl introduces conflicts, but it may take a while for that to happen for some people.