I suppose it depends on how the fatalities occour. I mean, if you do an Earl Docherty then chances are that a helmet and gloves won't do much. In a forced landing into a swamp then a helmet may save your life.
There are some interesting statistics from the NTSB (latest document is 1997) which can be seen at:
http://www.ntsb.gov/publictn/2000/ARG0001.pdf
Although this doesn't give any indication of whether a helmet would do much good in a crash, it makes very interesting reading.
Cheers
EA
