Perl is certainly a productive language, but people can and do write large applications in languages like C++. That's how most open source apps get started. Not Mason though. That was a collaboration before it made it to CPAN and is even more so now, with Dave Rolsky taking on a lot of it. And of course the work on "big parts of Perl" is done in C, not Perl.

I think that the key to Perl's productivity is easy data structures and CPAN. Standing on the shoulders of giants makes it possible to do amazing things "alone" when in reality you're collaborating with a few hundred people.