http://sports.espn.go.com/nfl/news/story?id=2481004
ESPN: It's not the law in Pennsylvania to wear a helmet. Why don't you wear a helmet?
Roethlisberger: Because you don't have to. It's not the law. If it was the law, I'd definitely have one on every time I rode. But it's the law and I know I don't have to and your just more free when you're out there with no helmet on.
That about sums it up right there. Common sense takes a back seat to the wind blowing in your face and "it's not the law" Granted, he wasn't popping wheelies or doing doughnuts in an empty parking lot a la KW II but still the very least you can do is just put the helmet on. So even if the accident isn't his fault, at least he's taking measures to be as safe as possible