I can call my friend a 'retard' (I don't, as a result of habit/upbringing) but I had a professor once who had a daughter with CP. I would never DARE say that word in his classroom (or any other, really) not just because of the offense it would cause, but because it has no place in a scholarly discussion.
Know your audience - trying to make a splash by saying something crass or unnerving just to watch people squirm is a fun game and it has it's place - but that's not really what the TED stage is for. Granted, I'm not qualified to make that distinction, but I think Chris Anderson (if anyone) probably is. The tone at TED is generally challenging, but tempered with a good dose of respect, which Sarah notoriously lacks.