Servlet technology lacks the rapid prototyping that a scripting language allows. I've spent 3 weeks developing a prototype that would have taken days in Perl.
This may be true for you, but what about a company where everyone knows servlets inside out, but barely anyone has written any Perl? When making these decisions one should keep in mind the skills of their employees. Of course, in many situations it's worth it to train employees, if the language/product/whatever can get your job done sufficiently easier.
The money you've saved could buy you a better network, pipe and more 'puters.
Excellent point. Developer time is almost always far more expensive than hardware and bandwith costs. It's a pretty safe bet to try and minimize the former with a small investment in the latter.