There are certainly reasons for not having a cutting edge Perl (or any other program) on your mission critical machines - since said program is so new, all the problems may not have crawled out of the woodwork :-)

However, there is also an argument for having a moderately up-to-date version of most programs - you want to upgrade when there are security problems with programs (IIRC Perl v5.004 had problems), but generally security/bug-fix reasons are about the only time to upgrade.

Upgrading only to fix security holes is not the same as never upgrading.
I'd be quite worried if the system never got any upgrades over a substantial period of time.

Cheers.

BazB