Yes, there are several legacy systems where a full rewrite is way more risky than maintenance-and-minor-enhancements-only. If you're surprised that Perl is still alive, don't go asking about how many COBOL systems are still out there!
Perl has libraries for numerical/science stuff too. :)
http://search.cpan.org/dist/Math-GSL
Those are some of the major ones. Being Perl, of course there's more.