PHP functions don't return 0, either. They return `false` which is easy to distinguish from other false-ish values using the `===` operator. They're still overloading `false` with failure, of course, but it would be unfair to say that PHP conflates all the false-ish values.
On a little more serious note, Perl is an earlier language and even more closely tied to C tradition. Many (but not all) of its built-ins and library functions and methods return undef rather than 0 for failure.