Emacs integrates well with Unix software that does one thing and does it well. You can even think of it as a buffering super shell with Lisp programmability, and use it to integrate and automate complicated tasks and put a usable UI on them.
I'm saying it's not because it has stuff like text editor, games even email client built-in (need confirmation never seriously used emacs), if it's only a scripting + text UI engine and offering all other apps as optional plugins then I'd agree it's "doing one thing".
I'd say facilities for text editing (buffers, kill rings, etc.) are built in, but nearly everything else -- the different modes for programming languages, games, mail, web, and IRC clients, etc, are all in Emacs Lisp.
