I still don't quite understand why perl doesn't seemlessly translate \r\n to a \n.

Presumably, the perl that codepad.org is running is a Unix-built perl, which means it does not add a :crlf PerlIO layer to file handles by default (as is done on Windows). The :crlf layer is responsible for transparent \r\n <—> \n linefeed translations (see PerlIO).

Adding binmode DATA, ":crlf" before slurping in the data should emulate Windows perl behavior on codepad.org.