[classichasclass]

> They added universal binaries to make the transition between 32bit and 64bit seamless.

Not just 32 vs 64-bit, but entire architectures. Mach-O universal binaries originated at NeXT, where at one time a binary could (and many did) run on SPARC, PA-RISC, x86 and 68K. On http://www.nextcomputers.org/NeXTfiles/Software you can see this in their filename convention: the "NIHS" tag tells you which architectures (NeXT 68K, Intel, HP, SPARC). The binary format carried over into OS X, where it was secretly leveraged as part of Marklar for many years.

In fact, Universal even on OS X really meant PowerPC and i386 at the beginning of the Intel age. It eventually morphed into the present meaning. I even maintained a fat binary with ppc750, ppc7400 (that is, non-AltiVec and AltiVec) and i386 versions.