In the early days of my freelance experience, a very wealthy man in Santa Barbara hired me to help him polish up a number of business documents. I think it must've been his very wealthy wife's idea, because one day as we worked in his glass-walled, mountain-view office, he blurted out, "I don't see why I can't just use Word to spell-check all this stuff!" As he was saying this, I'd happened to be making a note on one of his spelled-checked business letters that referred to "pubic speaking." Pubic speaking.
When I mentioned this amusing (and catastrophic) evidence of the spell-checker's egregious lack of contextual insight, he blushed, sighed, and muttered, "Geez. All right."
And that's why you need a competent editor and proofreader. Because spell-checkers suck.