I specifically stated in a later paragraph that high-performance items should be written in C over Perl. (I make no statement about any other language in that sentence.)
You were specifically talking performance in that chunk of caveat. I wasn't necessarily--I was talking about ease. There are things that are easier in C than in perl, even when performance requirements are factored out.
Also, as to this:
As for writing interpreters in one language vs. another ... I'm going to suspect that writing the parsing portion for an interpreter is easier to do in Perl than in C, simply for the string manipulation functions.
That turns out not to be the case. There are a number of styles of parsing that are easier in C than they are in Perl both as hand-rolled parsers and taking the language as a target for a parser generator.
I'll reiterate--you may think that perl is easier than C in all cases, but that turns out not to be the case.