We should cut him some slack anyway. I'm pretty dang good at grammar and you've corrected some of mine here. I don't ever take offense because no one can be grammatically correct all the time. There are way too many rules, and they're constantly changing.
The things I am hard on people for are run-on sentences, sentence fragments (sentences without verbs), and homophones (they're/their, your/you're, it's/its, to/too/two). Those are all things that never change that we can all learn to use properly.