Why so many spelling and grammar mistakes in Yahoo Answers?

When choosing a Best Answer or judging the credibility of the answer, I always consider the spelling, punctuation, capitalization, grammar, etc. of the answer. To me, they are an indication of the education level, interest, and intelligence (and probably age) of the answerer. I think that there are many non-native English speakers here, and many of them communicate quite well. But there are also a large number of kids who are too ignorant or lazy to try to express themselves according to established convention. They use their own "Webspeak" to differentiate themselves from adults and form their own community. But I think they're in for a big shock when they enter college or the workplace where the ability to write clearly, concisely, and correctly is a major factor in success.