XML::Simple requires an XML parser. The XML::SAX::PurePerl parser is the slowest, but it might be good enough for your purposes. There are also the expat and libXML C libraries (libXML is considered faster, expat is older and considered very stable). Anyway, you will need a working XML::Parser with expat, or XML::SAX with XML::LibXML (with libXML) or XML::SAX::Expat (with expat) or XML::SAX::PurePerl.

ActiveState installs an XML parser with its distribution, so that's why it works there with no extra effort.