Is that in order? I tend to use Helvetica first so Mac users don't have to endure Arial, then I add , my fallback for Linux, then Arial, then whatever crap your browser uses as a default (I assume it's crap but hope it isn't).
OSX users are such a small minority, its hard to find a way to please them without making it worse for Windows and Linux.
That, and I've viewed my website in Safari on OSX, it looks correct (although, like everything on OSX, it has hard to read fuzzy fonts).
There are many more OSX users than Linux on the desktop.
http://www.netmarketshare.com/os-market-share.aspx?qprid=9