I imagine that is at least as much a feature of the type of programmers that self select to become "functional programmers" as it is a feature of the inherent advantage of function programming.

I worked with a guy who was an serious Lisp-hacker who could do fantastic things in Lisp and was always advocating that we do certain things in Lisp. But he was also a great programmer when 'forced' to use C++ or Perl, he just grumbled more while programming.

At the risk of exposing myself, I’ve had to jump in and make changes to Sigma on several occasions. It was painful and I am not convinced having it in Haskell did anyone a favor.