You'd be really, really wrong about that. Us writers hate using our mice when not necessary just like everyone else.
WYSIWYG can break up thought process when done poorly. And in the age of the iPad, nobody's really done it very well at all. It's kind of a relic because it doesn't translate well to touch.
Also, don't let the tagline fool you: Mou has a big audience among writers.
Mou's tagline is "The missing Markdown editor for web developers."
I would have thought that a writer's needs would be well served with something like Aloha Editor and it's friends/competitors.