Well, in his case he was an experienced acrobatic RC heli pilot flying in a sanctioned location. Freak accidents happen and when it involves a large scale RC heli, things can go bad very fast. Heck, even medium-large quadrotors can rend flesh quite easily and the small ones can do enough damage to make you respect them afterwards. I have a micro sized quad I fly in my yard because I'm not comfortable flying the larger ones anywhere near people.

EDIT: Also, according to witnesses, the top of his head was 'gone', so while not decapitated I guess, it was basically the same (if not worse).