There are several perfectly valid reason he would want to do this. I will give the one that has come up more than once:

Not all software is developed for in house use, which can lead to following problems:

1. Many people (clients) don't understand the concept of an interpreter (Why can't I just click on it? What is that black DOS window that pops up, etc)
2. Deploying the Perl interpreter on many machines could become a large task.
3. Even if they have Perl installed, you have to be sure they have all the modues you need (Tk, LWP etc)
4. It is ever so much easier to deliver 1 executable file, rather than a host of supporting modules as well as the whole Perl interpeter.