Came across the 40 yr research on ski helmets on which I believe the OP's NY article is based. Both articles pretty much tell and conclude the story. http://www.lidsonkids.org/?p=358
1) wearing a helmet is better than not wearing a helmet--no question about it. Helmets protect against head lacerations and skull fractures
2) however, ski helmets don't protect against severe concussion, which is a more frequent and severe type of head injuries on the slopes
3) helmeted skiers ski faster, and the severity of head injury is higher for helmeted skiers although the overall number of head injuries is down. It could be that helmets alter the behavior of the helmet user OR that faster skiers are the ones that wear helmets.
Takeaway - always wear a helmet but ski as if you were not wearing one.
NOW I am just totally confused. Helmeted skiers ski faster, faster skiers have more severe head injuries. Crap guess I will have to slow down and not wear a helmet, oh crap I'll just quit skiing.