I had been wondering about the duck bill on the back (duck tail?) and so when I was at a dealer event that had a factory rep for one of the helmet companies, I asked him about it. They're there so you can use goggles with your half helmet.

 

I too have bad discs in my neck, and have found that my full face does not hurt as much as my 1/2 helmets. the wind rides around the full face better, and catches and pulls on the halfs, causing my head to move around a lot more.