Homebrew has become the most popular and most important package manager on OS X. More people use Homebrew (and consequently have invested time learning how to use, configure and modify Homebrew) than use Emacs. Although I know that the following opinion is subjective, I am tempted to assert that Homebrew is more important than Emacs -- not only more important than any package manager implemented in Emacs Lisp, but also more important than any Emacs package or any file or coherent collection of files of Emacs Lisp code.
I have installed a few packages into my emacs using package.el (which comes with Emacs these days). I don't like package.el very much. All I can remember (in the 20 minutes or so since I started reading this story on HN) about package.el without looking it up is that M-x list-packages is often useful as a first move in trying to get package.el to do what I want. Most software distributed with Emacs by the FSF is well implemented, but a lot of it is also poorly designed.
Don't get me wrong -- I'm not going to stop being heavy Emacs user any time in the forseeable future. It's just that I've learned long ago that it is a waste of my time to learn or master all of the functionality distributed as part of Emacs.
One more thing. At this moment, I have 32 Homebrew packages installed. My memory tells me that I have 2 or 3 packages installed in my Emacs via package.el, but my memory is unreliable, and there is no way in hell I'm going to invest the tedious time and mental energy required to figure out how to get Emacs to tell me how many packages I have installed at this moment. In contrast, my determining that I have 32 Homebrew packages installed required almost no thought at all. Right away I knew how to get the information, and the whole process took me at most 5 or 10 seconds.
It involved the command line "brew leaves". I dont have "brew leaves" memorized, but I knew that somewhere in my .emacs.d is a call-process call to /usr/local/bin/brew that essentially lists all the packages I have installed, so searching my .emacs.d for the string "brew" got me the information I needed (namely, the Homebrew command is "leaves") in a matter of seconds.