Some day, somebody will invent the perfect all-sport helmet. But it hasn’t happened yet. Helmets for cold/wet conditions — skiing, kayaking, that sort of thing — need to have closed-shell construction. Helmets for aerobic, warm-weather pursuits — such as cycling and skating — need as much venting as possible. Helmets for rock climbing generally fall somewhere in between. The Petzl Meteor ($75) does a pretty good job of straddling that divide, but is essentially a light, well vented climbing helmet. I couldn’t imagine wearing it on a bike for any more than a short ride. Really, I think cycling helmets come closest to what you need for skiing. You can always put a helmet cover over one to cut down on the breeze, plus wear a skullcap of some sort. So spend $65 for a Bell Image Pro 2000, get a $15 cover, and do your thing.
Moreover, while I wouldn’t suggest NOT wearing a ski helmet, I don’t see any compelling reason why one should — and I say that having looked into the issue. Head injuries are quite common in cycling, but rare in skiing. Moreover, in those cases when a head injury while skiing does result in a fatality or serious injury (in recent years, the deaths of Sonny Bono in 1997, and Michael Kennedy a few weeks later come to mind) were the result of direct, head-on impact with a tree. No helmet in the world is going to save you when that happens. Moreover, especially in children, there is some evidence that a helmet increases the risk of injury because it can cause the head to whip back and forth during a fall, damaging the neck and spine.
I always wear a helmet when cycling, and often when climbing. I don’t wear one yet when skiing, and ultimately may never do so. But that’s a decision everyone should make on their own.