I agree with this entirely, misuse words not only reduce the quality of a post, it can also scrabble the real meaning of the post such that it becomes difficult for others members to decipher the point being made.
Also, Spelling Checkers are great when it comes to checking words' spelling, but they are just what they are "tools", just like what a cutlass/hoe is in the hands of a farmer, especially when it comes to grammar. I've used some of these tools and often times grammatical errors still pass through them.
So, English language skills is still an important element and most importantly, proofreading over and over before posting.
There is a "preview button" next to the "post button" in the reply form, it's not there for decoration, you should learn to click that first and go over your post like twice. Equally, posting your reply is not the end, you can still go over it again.
I can't even remember how many times I read over my posts, sometimes. Well, you can't be too certain, most times your fingers are not exactly typing what your mind is telling them.