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".
What you are pointing are the hard ones. I mean, even those that are born having English as their first language also do not know the difference between affect vs effect and ensure vs insure or in spite of vs despite.
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.
I agree on some point. (but with reservation to avoid the fallacy of hasty generalization). I also notice that some mobile users tend to commit grammar errors and even spelling because of the auto correct function in their mobile phones. They need to turn it off prior making a comment.