I've heard that too. It goes along with the argument of the helmet causing hidden brain bleeds that painfully kills you days later...Those comments typically come from harley types or squid racers that wear a doo rags instead of helmets. Additional discussion on the subject with them indicates they are either justifying their desire to not wear crash gear or have been brainwashed for years by those same individuals. Further rational discussion isn't possible because no matter how calm and sensible you are, they resort to screaming and yelling that you're wrong and an idiot and they know they are right no matter what.
I'm calling hogwash on that rumortheory though. Consider that any head hit hard enough to break your neck will have almost certainly have compromised the structural integrity of your skull long before your neck snaps. Personally I've walked away from a fatal head impact crash without a crushed skull or broken neck and had nothing more than a very light headache and a 5 minute trip to the chiropractor for a pinched nerve in my back...and $350 out of the bank account for a new helmet plus about $150 in motorcycle repairs. The rest of the crash gear was just dirty from the dirt and rocks I went through, no damage and no road rash. That was over three years ago and there's nothing wrong with me now that wasn't already there before the crash.
When it comes to it, this is all that you truly need to know about the whole helmet vs no helmet discussion. You don't even need to understand Portugese to figure it out:
http://www.youtube.com/watch?v=9P-1a_e_Yz8