NoCrying I didn't get the impression as much of "poor spelling = thick" but more the idea that "poor spelling, but don't bother to have anyone proofread your official documents for spelling/other errors prior to releasing it to the public = thick." In other words, some people struggle with spelling, this happens and there are genuine reasons for it. It doesn't make them "thick." And I'm saying this as someone who generally has good spelling (I say this as this means I will likely MAKE a spelling mistake the moment I say I spell well 
) and also has one child with severe dyslexia who cannot spell well at all - so I get both sides here.
Again, poor spelling does not mean someone is thick. Of course not. If you are, on the other hand, a poor speller for whatever reason and you do not have someone with excellent proofreading skills look over your government document before releasing it to the public... well, I'd have to say I don't think THAT is very clever.
A very distinct difference.