haha, I ride a motorbike as well and wear a full face helmet (superbike on European roads), and yes you can go fast but, unlike on a snowboard, you keep your head relatively straight (probably turn it +/- 30 degrees whilst cornering at speed). When snowboarding your head and neck is a lot more dynamic and you turn your head a lot further.
The fact that you're comparing riding a motorbike and a snowboard is idiotic!
So you're saying that with a full face helmet you can't turn your head? Have you ever watched a supercross race? How about MotoGP? Ever see rossi turn his head nearly 180 degrees? But that's impossible with a fullface... You're very naive.