[tptacek]

Extensibility is the reason for Emacs' power. Lisp is just an implementation detail. You could make an equivalently powerful editor in any high-level language.

There are other extensible editors, but the line between Emacs' kernel and its extensions is drawn at a different place in Emacs than in any other popular editor. It is more likely that any given feature you're interacting with in Emacs is provided by its extension code than it would be in another editor.

Probably more important is the benefit Emacs gets from being one of the two major Unix editor projects. It has an immense community and user base.