So, I suppose for MacPerl the IO layers must be capable of translating "\x0D\x0A" and "\x0A" to/from "\x0D" to allow for reading "foreign" files

Nope. Well, probably not what you expect anyway. MacPerl (to the best of my knowledge) doesn't by default translate foreign line ends - it just DWIM for native (pre OS X) line end characters - \x0d.

You can of course use the :crlf file I/O translation layer to do the business, but the default behavior is to treat "native" files as you would expect because anything else is tricky or impossible. perlrun's PERLIO section, binmode and of course open are likely to be of interest too.