My experience with school communications and online forums has been that whenever someone criticizes someone else's graofftopicr or spelling, they have invariably, in the act of correcting, made a mistake of their own. It's a form of cosmic irony intended, I believe, to keep people from being a-holes.
I've noticed many errors in the letters I get from my kids' teachers. If I were an ass, I could have sent a note about proofing their work. Fortunately, as bad as I may be, I'm not THAT guy.