Mac OS X 10.3 did have support for fat binaries, it supported both ppc and ppc64 (although there were very few system libraries that could be used from ppc64).

Mac OS X 10.3 did have support for fat binaries, it supported both ppc and ppc64 (although there were very few system libraries that could be used from ppc64). Mach-O fat binaries date back to NeXT though, since NeXTSTEP ran on many architectures (there were quad-arch apps back then which ran on i386, m68k, hppa, and sparc).