Neither "XOR" nor "encryption" may be found in the perl2exe docs. It's just something you may find out while trying to break into the EXE. You are right that PAR is more clear about what is it doing, perl2exe doesn't say pretty much anything about what it does.
IndigoStar says: "Perl2Exe is a command line utility for converting Perl scripts to executable files.
This allows you to create stand alone programs in perl that do not require the perl interpreter. You can also ship the executable file without having to ship your perl source code." They do not even mention "compilation" on the page. (They do use the word a few times in the docs though.)
IMO they did not mean the XOR as a means of real encryption, but just to prevent the text to be seen in the EXE and found by normal "Find in Files". Just a means to prevent the code from people that would have no use for it anyway.