jcwren quite astutely points out the other side of the argument, but don't forget to read the part where he says he's using some outlandish examples.

The important thing to remember about modules is CGI, LWP, DBI, and the XML::Parser. Unless your first name is, say, Lincoln, Gisle, Tim or Alligator, or Larry, you're not likely to sit down and write a module with that much functionality and quality from scratch. (These people tend to have the kinds of jobs where they don't have to fight over installing a module or two.)

There are a handful of very important modules that do their jobs so well and so completely that not using them is not only costly in terms of time and labour, but even hazardous from a security standpoint.

I think most managers who fall under the category you describe just don't realize how tricky it is to read an RFC and implement it in a useable and workable way. They wouldn't ask you to write a web server, why would they ask you to write your own code for handling CGI?