You guys are missing the point - a spell checker won't flag a word like "effect" or "insure", when really what you mean is "affect" or "ensure".
Yes, I understand what you`re talking about. The problem you raised can`t be solved with electronic spell checking applications. People who make this type of mistakes, most often don`t even worry about the quality of their posts. They just don`t bother what and in what form they express, the most important thing for them is the fact that a comment has been published, which can be counted in the bounty campaign. Those who are really worried about how their posts will be perceived by other participants, re-read them several times, editing and correcting their thoughts.
Or maybe the situation is completely different. It`s likely that in such cases we are dealing with Freudian slip. In appearance, insignificant and meaningless erroneous actions serve to realize unconscious desires. Despite their seeming absurdity and innocence, this is an outward manifestation of subconscious conflicts and repressed desires. People may have unsolved psychological problems, and we just blame them for their poor knowledge of the language.