It's not just Linux distros. Mac OS X (not sure if it's base OS X or the developer tools-- I haven't had a machine without dev tools in ages) still ships with old versions of Perl. Snow Leopard has 5.8.9 and 5.10.0. It looks like Lion is up to 5.12.X, and it wouldn't surprise me if it's still got 5.8.9 in there, too, for some legacy functions.

But with a Mac (and probably any other OS that comes with a Perl install) it's highly recommended that you don't touch any of the system installs, and install your own instead. Anything you do to their installs isn't guaranteed not to be overwritten by some future update. On snow leopard I mostly got away with installing into the 5.10.X, but found that it behaved a little wrong with some modules. I've since switched to Perlbrew and it works well.