My point was the legacy is there and it's pretty large, should not be understated. Apple may not care so much about compatibility between releases or with NeXT binaries from 1987 (though I don't think Windows code from '87 works so well on NT either), but the old code is there and if your argument is that sort of thing doesn't help binary compatibility, then that's a problem. I was making my point in shorthand fashion, so I didn't even touch on Mach which is very old as well.

People have this impression that OS X is flashy and new and immune to or not experienced in code rot, and I didn't think it rings all that true.