I can't say if there was cause and effect, or even correlation, between the accident and the brand of motorcycle. No helmet use seems related to the results.
Call it anecdotal, but I've seen more Harley riders in states with no helmet laws choose to exercise their freedom to not wear a helmet than any other brand. If anyone else's anecdotal mileage has varied, I'd be interested in hearing it. I really would like to see such a study done scientifically, though. And I'd gladly wager that those, regardless of brand, who choose not to ride with a helmet are, just on average and not as to any particular rider, a bit more intellectually challenged than those who ride with a properly certified helmet.
To be both clear and fair, I have known MANY VERY intelligent Harley riders, too, including Board-certified physicians, attorneys, engineers, and folks with Ph.D's in scientific disciplines, and folks with no degree at all who just happen to be extremely smart. And some people who ride BMWs, Ducs and GWs are blithering idiots. I'm sure some people, somewhere, on one of those bikes/brands eschews a helmet. But I've never seen one in the wild.
Also to be fair, were it not for the cool factor of painted helmet designs, young sportbike riders might be exactly the same, and even then, I've seen guys on 'Busas riding with expensive helmets stuck on the side-rear of the bike.
But if your point is that by FAR the most reasonable factor to use in determining whether an accident is survivable is helmet use, regardless of brand, I'd agree, and I'd hope like heck we all would. That's the most important point here. Wear a dadgummed helmet. That's a no-brainer, pardon the pun.