No, you are correct. That is a VERY extreme example.
And I still also agree that people do make mistakes, especially on message boards.
However, people who are accustomed to using poor grammar begin do it like a habit, and will eventually continue to use it in every situation. People who spell poorly AND do not use spellcheck WILL end up with poorly spelled professional documents.
The simple point I am trying to make is that if you don't train yourself to use proper grammar and spell things properly OR use available resources (like spellcheck) to help you; then people will assume you are not as intelligent. Yes, my example was extreme, but the point still stands.