The fault isn't necessarily poor spelling here. I think that the problem has more to do with typing than anything else. Too often people get very relaxed when writing emails or responding to threads. People don't take the time to review their words and end up looking silly with sentences like "I woked the dwg ths mouring..."
On that note, often people use the wrong form of the word--spell check won't fix that, nor will it fix the poor grammar.