I'm guessing that there are such things as core modules in a perl distribution to provide...

• A stand-alone useable installation (once compiled & installed) - providing a far simpler introduction since the intending user wouldn't have to download & install the perl compiler/toolset and then subsequently download & install modules - some of which may not work with the (version of the) toolset
• To provide a baseline of the above in order that the usability can, as far as humanly possible, be guaranteed and maintained with the distributed modules

Recently I worked on a Solaris project (which uses ABI standard packaging) where I/we designed

1. A package for the distribution plus a package each for the non-core modules
2. A build process that downloads and translates the perl distribution (& modules) into packages for subsequent deployment and installation onto the target

Or, put another way, designed our packaging to supplement, not ignore, the significant benefits of perl & the CPAN - why re-invent the wheel when perl/CPAN already has the majority of dependency tracking etc. implemented, all you need do is supplement the given dependencies where dependencies may be missing in the original.