I re-read your post and wanted to clarify what you meant by:

  Apple (and previously NeXT) inarguably demonstrated its
  value and ease-of-use over the past 20 years. Producing
  x86-32, x86-64, armv6, armv7, and PPC binaries all from the
  same source code -- and having them work the first time --
  is incredibly simple on Mac OS X.

Presumably you aren't under the impression that FatELF has anything to do with making source code easily compile to more targets. FatELF merely allows you to combine the binaries that would result from taking a source code base and compiling a binary for one arch and then another and gluing those together into one file.

The wording on your post wasn't entirely clear, though I'm guessing we're on the same page.