Maybe it's just a joke, but for those that don't know that is Perl's motto and even better because there's the venerable, wonderful CPAN [0] which is the de facto package repository for the language.
The Python's motto was created as an obvious reference to the Perl's one, purposefully negating it.
"There should be one-- and preferably only one --obvious way to do it."
That is different from "there's only one way of doing it" in so many ways that it's not even funny.
So, not completely serious, but not just a joke either. Python isn't exactly a "reverse Perl" but it's close to it, and it's a really good language.