Question:
Also, the "savings in medical costs" are not the whole story: what about the lost productivity and time off of work, not to mention putting up with a possibly painful injury?

The vast majority of such accidents don't involve head injury. The majority of bike crashes where the rider has a serious head injury happen as a result of bike-motor vehicle crashes. If people are worried about preventing serious head injury, it's important to look at the accidents which cause serious head injury.

Answer: That sounds a lot like the Rivera etc al. site or someone using their figures. Those figures are quite controversial as is the original study that I have read [Thompson, Rivara, & Thompson (1989 ) A case control study of the effectiveness of bicycle safety helmets' New England Journal or Medicine. 320 1361-1367]

I believe there may be some methodological and/or interpretive problems with this research . Others are more up-to-date with the research and I am sure can comment more effectively on it. However if you get a chance have a look at the above paper. I just had a glance at it yesterday and I cannot even determine who among the various levels of injury were or were not wearing a helmet. It may be there but it does not seem obvious.

The Abreviated Injury Scale does not seem to be doing the same thing as the types of injury. If you look at Table 1 there are 111 forehead injuries but only 109 forhead injuries rated as Forehead Injury only with an AIS score of 0 . Seems logical but the type of injury (Brain, scalp forehead ear death) are not the same as the severity scores . Interestingly your quote gives a 3 point scale. The 1989 paper gives a 6 point scale (0-5)

BTW the 3 Deaths "All had severe head injuries " but one (who was not wearing a helmet!) died two weeks after discharge of a pulmonary emolus and the second died from a ruptured myocaridoum This does not invalidate the injury of course but the deaths are interesing. I don't think a helmet protects heart muscule.