The reality is any/some/all of the reasons above apply to any combination languages in your question. Might as well ask "Why are programmers still using COBOL rather than Erlang?" Because.
When I'm writing scripts that can be run on any given system, there are very few things I can use that I know will work. One of those is Perl (5.8.8) and the other is Korn Shell (ksh).
Perl 6 being an entirely different beast from either of these two languages, of course.
Here's your magic methods and properties: http://www.rafekettler.com/magicmethods.html
Those magic methods kind of remind me of clever hacks while coding in PHP.
Self is one of those things, if you wanted to you could easily add another instance variable, just implement getattr and have it return a partial function. Although I will admit it is one area which does cause more than its fair share of errors, but I prefer it to Ruby's methodology.
Unlike... Perl?
A lot of people find Python's scope rules annoying.
I've heard Perl has the best unicode support.