No-one is saying that these things don't matter. I admit to being a pedant and cringe sometimes, when reading posts. However, it is rude and unkind to point out a poster's spelling or grammatical errors (as has happened here on a number of occasions) on a public forum. Everyone should feel comfortable posting on this forum.
As for teachers not making errors, of course we should expect high standards from educators. However, we are all human and mistakes can happen.
I wish I could be as perfect, but not as smug-, as some posters on here.
This comes from a retired teacher, who specialised in working with pupils with dyslexia (my daughter included).