There was a period of time, not all that long ago, when high school English teachers decided to grade an essay only on content. The mechanical errors would be overlooked so that the students would not feel discouraged. No, it wasn't in every school across the nation but in enough of them that it became newsworthy.
When this all came to light, I seethed inside and bellowed about it bit outside, too. Good writing, for me, constitutes both content and the mechanical side. No matter how good the content is, if there are multiple spelling errors, tense problems, wordiness, verbs and subjects not in same tense, punctuation problems, then the content definitely loses something.
Years ago, some writers didn't bother with making all those mechanical things just right. They had editors to correct all that.That was the attitude some writers had. Maybe some of the editors did the corrections but in today's world, editors aren't going to give a second look to a piece that is fraught with mechanical errors. Publishing concerns, whether books or magazines or ezines, hire the fewest number of people they can which means the editors don't have time to deal with those little errors. That is up to the writer. Personally, I think it should be the writer who is responsible.
The poster on spelling peeves above shows ten of the top errors people make, and they make them over and over and ... Those who write on a computer have the luxury of using the spell checker when they finish writing. If you write on Office Word, you can check both grammar and spelling. But it's up to you to take advantage of those little help aids. If you write on a program other than Word, you most likely have the spell check/grammar help option. Even if you consider yourself A-1 in this department, it doesn't hurt to make that check before you submit your work.
The poster only covers common spelling errors. Remember that the mechanics of writing entail far more than spelling. All those items I mentioned in paragraph two and more are included.
Confession Department: I don't always do this myself but I know I should. I find that most of my errors are typos but they don't look good in a final document. I know that and I need to listen to my own advice here and take those few extra seconds to do a check. I'm going to try to be more diligent. How about you? Care to join me?