I believe that's wrong, actually. pf, for the uninitiated, comes from the OpenBSD project. I run all of my company's firewalls with OpenBSD and pf handles my nat. Now, I admittedly haven't tested out pf on my Mac, but according to the pf.conf man page on Apple's web site, their pf implementation does support nat. I guess maybe natd is redundant...? Don't know.
pf takes a little getting used to, but it's the best firewall I've ever used. It really is pretty awesome. Hopefully in the future, Apple's pf will get a little closer to the version in OpenBSD. Currently, Apple's is several years behind.