You have to understand, I'm not one of the people that runs around getting a little chubby every time I correct an apostrophe or an "ie" to "ei", because I don't do it because it's fun. I do it for several reasons, depending on the situation.
1. If the person is someone I think has potential to be an intelligent, funny, witty, or otherwise positively contributing Escapist, I don't want them to be banned because of a post having too many "Lol"s and "wtf"s in it.
2. If the person is a non-native English speaking person, they may honestly not know that their spelling or grammar was incorrect. In which case, if they are seriously attempting to learn English, being told (politely, I might add) that they made a mistake, what the mistake was, why it was a mistake, how to fix it, and how to avoid it in the future will help them learn the language.
3. Proper grammar and writing abilities are crucial to success in the modern world. If you can't write a resume or job application in proper, intelligent English, then you WILL NOT get the job. Not even if you're overqualified 5 times over, if you can't write correctly you will lose the job. And by allowing yourself to relax your standards because "its t3h intarwebs, who carez?", you are not only setting yourself up to relax them again later when they are necessary, you are also forgetting that employers these days actually LOOK for your presence online. I have had a friend be turned down for two jobs because of the way he wrote on his Facebook page. Yes, it's the internet. And people DO care. Just not as visibly as in real life.
Yes, it irks me when I see improper grammar and spelling in general. Yes, it annoys me when I see it used poorly time and time again, with complete disregard for what is or isn't proper English. And yes, I do get a sense of joy when I help someone improve their grammar and they listen. But that is not the reason I do it. I do it because it is beneficial to everyone that it be done.