At best all they can claim is A it's not so much whether most of them are accessible as if the code is valid. Few use valid markup by default so their accessibility cannot ever get that high by default.
Yes it usually easier for humans to make mistakes; usually it's because they either don't care about validation, or haven't the time (or inclination in some cases) to check their output against the strict markup grammar rules.
That's great info. I did wonder about the mark up side of things. Do you know why most people don't use valid markup for forums - is it just easier to programme that way?
Legacy programming, I suppose. It's harder to create something from scratch. I have been struggling to convert a relatively simple guestbook to valid markup - though I am a user not an original programmer. I guess forum coding must be a big job.