This is what I was thinking too, as a Norwegian that's been skiing my whole life. A 15-mile trek in temperatures close to zero F is not something you'll do lightly. Sounds like at least the trip leaders were in great physical shape but not with the right equipment for this kind of trip.
If you're going in conditions with lots of poweder snow and no trails, you need proper mountaineering skis if you want to do it halfway comfortably. E.g. something like this: http://www.asnes.com/produkt/combat-nato/, that's sufficiently wide and works with skins in rough terrain, etc. Otherwise you'll sink through on every step and waste lots of energy. Also, as you say, the boots are better insulated. Standard touring BC bindings will freeze if you get snow in them, making is tough to get your ski back on. Taking off your skis and walking when the snow conditions are anything less than hard and frozen? Sounds painful.
If you're going in conditions with lots of poweder snow and no trails, you need proper mountaineering skis if you want to do it halfway comfortably. E.g. something like this: http://www.asnes.com/produkt/combat-nato/, that's sufficiently wide and works with skins in rough terrain, etc. Otherwise you'll sink through on every step and waste lots of energy. Also, as you say, the boots are better insulated. Standard touring BC bindings will freeze if you get snow in them, making is tough to get your ski back on. Taking off your skis and walking when the snow conditions are anything less than hard and frozen? Sounds painful.