There's no need to blame non native speakers(like myself) for a few typos. Correcting spelling mistakes doesn't make yourself more readable. If the content is really unreadable, I'm not sure that a spell checker will help.
Moreover, adding a spell checker in a forum will not make it really user friendly. If you have to correct all spelling mistakes before posting, how would you feel after a few posts ?
Also keep in mind that while a spell checker is good in theory, a code centric discussion forum probably isn't a good fit. Think about how many spelling mistakes a spell checker would pick up in code we post?
I think most spelling mistakes are probably just typos and/or members still learning english and I don't think any less of anyone for such things.