Why? It's good system administration, that's why. As I said in my original post, "rolling the dice is for role-playing games, not work!" In other words, you do not leave things to chance for things running in production. If you cannot grasp that concept then you just do not have enough system administration experience. You may want to read some "best practices" type books, such as "The Practice of System and Network Administration 2nd Ed" (publisher and Amazon links). Or work in a shop with several other developers and multiple Perl installations for some hands on experience.

Your argument against a "fragile" wrapper script makes little sense because the entire system is "fragile". For example, you are concerned that an upgrade may break your wrapper script when an upgrade to the system will more likely break your Perl script.

Your argument against a big complicated wrapper script also does not hold water. If the environments your code may run in are that different then you are going to have to do something about it anyway. If not then it is not going to be a complicated script. You are also moving into the realm of distributing code where a build environment would be more appropriate. What do you think happens when you do a "perl Makefile.PL"? Or a "./configure"?? Someone else has spent time figuring out how to resolve environment related issues for you. Quite frankly, it sounds like you are used to using packages created by others and thus have not been exposed to the work that went into making them. Have you ever tried compiling Perl or GCC?

But at the heart of it all is that principle that you make sure you know what your production code is doing and what it is relying on.