vi is ubiquitous: you will find it even in the smallest distributions. It is much easier to use than its original forms, ed and ex.
As mentioned in on page 168 of your text, spell (or ispell, an interactive version) are usually used outside of vi.
emacs is a far more ambitious program than vi.
emacs is derived from teco, an even more cryptic editor than ed; the history of emacs is far more detailed than that of ed.
emacs has a distinctive look: