The CPAN issue's a generic problem with the old CPAN module--the first thing you should do is install the latest CPAN, and it takes care of that. It's an old CPAN.pm issue long since fixed. (Just fixed after 5.6.0 was released) The installed base is far less tiny than you might think, too. OS X does have some issues with some of the ancillary libraries (like Curses) but I've not had problems with anything that I've not had problems elsewhere with.
(Linux, though, is unix, as much as any other unix out there)