in the online world there is a broad spectrum of everything from personal blogs to million dollar news outlets and everything in-between. My impression was that this article addresses the lower end of "professional" writing and is intended to be both helpful and humorous. With that said, I have seen some rather glaring errors on major sites (Engadget, Gizmodo, and others) where eyes on the page equal dollars in the bank.
What happens in forums, comment sections and social sites is not so much "writing" as it is conversation, and the site owners are monetizing the users and not the content. There is no implied contract of "I'll frequent your site and look at your ads because I like to read your articles.".
So to sum up, my thoughts on grammar are similar to my thoughts on any profession; If you are a plumber you should know how to use a wrench, if you are a carpenter, you should know how to use a hammer, and if you are a writer, you should know how to use the language. If I am paying you, or you are getting paid for my patronage, then I feel I have a right to some expectations with regard to your use of your tools.
Like +Carta Brown
suggests above, in a forum like this, it is most important to get your ideas across. Compulsive proof readers like me just need to get over it.