Multisport, hockey, football and climbing helmets are not made to the same impact standards as they are made to take multiple smaller "hits", not one big hit.
Weight is very much an issue. Not that the weight has much to do with your total load but very much to do with the load on your neck so don't dismiss helmet weight as a non-issue.
Mototcyclists have a very different riding position than bicyclists so the weight factor is also different. A full face motorcycle helmet would provide better protection but you would find it intolerable after a very short time.
BTW, I'm a member of the "Saved By The Bell" club having distroyed a Bell helmet in an accident. I had a mild concussion that would have been anything but mild without the helmet. On the basis of one data (datum?) point I'm a firm believer.
This message was edited by DaveB on 5-26-06 @ 6:47 AM