I can spell well, but I don't type well, so my posts on boards like this are full of errors. I'm not particularly pedantic about checking my posts before I hit submit as it just isn't that important to me that everything I write is perfect (I have better things to spend my time on). As long as my message is conveyed and readable I'm not concerned. Sometimes I'll go back and edit my post if I find something that bugs me a lot in the post, but otherwise I'm not bothered.
I think there are countless reasons why people make errors in their posts and not all of them are linked to intelligence. I'd hold back on the judgements personally.