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For what you say about these statistics to be true, i.e that many of the recorded incidents involved no injury, it would make this statement above the stats a lie:
"the number of sports related head injuries seen in hospital emergency rooms:" Ambulance staff rarely take un-injured people to ER.
I think a bigger problem with the stats is they are not recorded against time spent engaged in the sport, or against number of individuals involved in the sport, without which they mean little.
I've fallen off my bike twice this week on the ice and I have a sore wrist and shoulder.
William.-
For cycling injury I'd suspect a great number went to emergency room for a broken wrist/arm/leg/collar bone/whatever and had head injury recorded as a secondary injury. Without a helmet they would examine and find nothing so record nothing, with a helmet they examine and find "well something happened as the helmet is damaged so I'm going to put broken wrist and minor/possible head injury". It's not a lie it's just how the results can be distorted by the way we record/examine/perceive things.
If you study statistics you soon learn it's very hard to isolate statistics well especially when taking them from another persons study where the means of data collection wasn't specifically designed to isolate the statistic you are interested in preserving.
Clockwise
This is one of those statistics where the method of recording greatly impacts the variance in data provided. Compulsory helmet use in sports cycling often results in a flimsy helmet becoming a damaged helmet during a crash and then being recorded as a head injury where no head injury was sustained as a possible impact is derived from the helmets condition, where in other sports no helmet is worn to act as an indicator and so the threshold for registering head injury is much higher. It's like if you walked around in a tissue paper suit and then went into hospital showing the tissue paper suit was ripped, any smart medical person would record "possible x" anywhere the suit was ripped even if just to cover themselves, exactly the same with helmets.