The best programmers use vi or emacs, because the most experienced programmers are the best, and 20 years ago, there wasn't much choice except vi and emacs.
After having started with vi (ca. 1987) on a machine with a very slow text terminal, I converted to (GNU) Emacs after a few years (on a faster machine), and used it almost exclusively for nearly 10 years.
Emacs was the first truly integrated development environment - the whole edit/link/compile cycle could be controlled in emacs, and you could roll your own for whatever compiler you used.
Nowadays, IDEs such as eclipse are even better integrated (to be honest: emacs sucks at graphics), but Emacs is still one of the best environments for "pure" text editing.
