A flying helmet does have marginally better noise attentuation than a headset and it does keep the head warm, although it is not always desired, especially in the summer. I think that comparing a motorcycle helmet with an aviation helmet is like comparing a farm strip with Heathrow - they are there for slightly different reasons. A flying helmet will stop you banging your head on the cockpit, ie relatively low energy impacts - it would hopefully stop you being knocked out and allow you to effect an escape in a forced landing/ditching situation. I motorcycling helmet is designed to stop taking road rash to the face at 100mph.
That said, the Alpha helmet provides a significant amount of padding. It took a little getting used when I first wore a helmet - now I feel naked when I fly without one.