Apple does deliver Emacs on OSX, but unfortunately a terminal window, character mode only version. What I use is GNU emacs, the Carbon port from Andrew Choi, who 'defected' to XEmacs; I do not have a standpoint here because I do not care and only want to use what works. Apple does have an Aqua port of Emacs on its website, that looks promising (great fonts!) but does not seem to be quite there yet.
What I would like to know is why Emacs, compiled from source on my own system, breaks on every OSX upgrade, now even from 10.4 to 10.4.1. I gather it has to do with C++ and GCC, which is changing its ABI every sub-release. Question that remains is why big apps as Motion and Office do not break.
For comparison, Java code keeps running all the time if it is post-1995-beta level. I've got mainframe (here we go again) load modules (what we would call binary executables) from the seventies that still run. This platform also switched from 24 to 31 bit addressing, and more recently to 64 bits. I guess those people were smarter.
This sums up the developements in the trade (a little jealous of someone else's tagline:
The old days: Smart People in front of dumb terminals
Now: Dumb people in front of smart terminals