i dont think style of bike usage should be ignored.
all cyclists are not the same.
most of us here ride fixed gears....likely, we ride them faster and more aggressively than the casual beach cruiser type or casual cyclist might. same applies to bmx.

the types of riders involved in accidents incurred during more aggressive riding would benefit more from involving a helmet than the majority of casual cyclists would benefit from wearing helmets.

i really don't think that's disputable. it's extremely biased to apply the results of a study who's participants are largely and on average much more of a casual (read as "slow and cautious") to this forum, primarily more aggressive, faster, riders.