Gotta agree with that. If helmets were changed to ensure they stayed on no matter what, the neck/spine would take the force and probably result in worse injuries (when comparing a face being cut up or a neck/spine being broken).
At the end of the day I think it's just a freak accident. Motorsport is dangerous, these guys know it and they choose to ride because it's what they were born to do and love. If you told Simoncelli he'd probably die if he rode, I'd wager he'd still get out there and race.
The sad thing is that if he had just dropped it, he would've slid straight off the track and maybe even got back on the bike to finish the race. The fact that he was still in the middle of saving it when he got hit, cost him his life.
It's a freak accident and no safety measures would have prevented it.
again, RIP Simoncelli