It's not so much that its presence is a measure of quality, as that its absence is a warning that the code's author may have been inexperienced in the ways of Perl. As such it's a code smell -- one of those little things that make the reader start to feel uneasy about the quality of what they're looking at.

Of course, I totally agree that it doesn't really make much sense to insist that they be included by law in all code posted here. I personally would only include them in a code snippet if I was posting something that was intended to be a complete module or script.