Well, you have to keep in mind that some of the people visiting these forums don't have English as their first language. Thankfully, alot of the time they post something at the bottom of the post saying "Forgive my spelling/grammaer, English is my second laguage" or something of that nature.
However, there are plenty of people who just don't care. They see the internet as a place where grammar doesn't matter, even though you're still using the written word to communicate. It sucks, but there's not really anything that can be done about it. I just tend to ignore the posts that take too much effort to read.
Lesson: If you want your ideas to be read and understood by people on the forums, please use grammar and punctuation. :)