I totally get using vi to write a book or something on an air gapped computer. No distractions. But not sure about WordPerfect. To each their own though.
The important difference (for me) is that a word processor understands proportional font geometries and physical page dimensions, so I can layout the page interactively. For example, I have some text that I want to fit on a single page of A4 in Helvetica 12pt, and I'm willing to edit it until it fits.
I think that's a really hard problem to solve in a text editor, but it's trivial in a word processor.
I also use WordPerfect for DOS, because it's a full-featured word processor that you can use in a terminal (I think the author of this site uses it in graphical mode, but I prefer to use it in an xterm).
Here's a screenshot, notice how WordPerfect knows where the text will wrap.
