Earlier quoted context omitted.
It's a fair question. Emacs is one of few editors left that makes it possible to work on multiple files at once without taking your hands off the keyboard. No fumbling with the mouse. Watch someone who has mastered Emacs edit some code and you'll understand its appeal.
Going a little further, Emacs is itself (at least a lot of it, including js-mode, for instance) written in Emacs Lisp. This makes most of it modifiable by its user. It's not impossibly hard either - I have made a minor mode for Pyccuracy tests in a couple hours. Learned some in the process. Even the "configuration files" are, really, Lisp code, not bags of values and options.
Vim configuration is also not a bag of options and values; by default, it uses vimscript. vimscript is an interesting language (supports a form of OOP) but only really usable in the vim world, so it is up to you if you want to learn it to do things besides assign values to options.
Alternatively, vim allows you to do editor customization in perl, and while I have found very little documentation for it, it also supports mzscheme.
How does this kind of thing help anyone? Why is Notepad just not good enough? You can add entire text-manipulation features to your editor, including Intellisense to your specifications, tools for refactoring, integration with other tools outside the editor, and so forth.
Both editors have large communities and have few real competitors for fast and powerful text editing (I hear TextMate comes close).