A bit of clarification is probably in order. When the NPS says the North Rim is "CLOSED", I think they mean that facilities are closed and roads are closed to vehicles. I don't believe they will bust you for simply going there, though they might ticket you for driving on a closed road. (hikermor or other please correct me if I'm wrong.)

In fact my understanding is that quite a few backcountry skiers visit the N Rim in winter. Case in point, some years back a friend of mine, a very fit and highly experienced backcountry traveler, skied in solo from where the road was closed to a N Rim trailhead, tied his skies to his pack and changed into hiking boots, and hiked down into the canyon and back up to the S Rim. My recollection is that he said the biggest problem was that the trails just below the rim were quite icy in spots and required careful walking. This is of course very different from inexperienced people driving down from Vegas, probably planning on taking a few selfies and then driving back to the casino.

I think the biggest thing these folks lacked was simple common sense. If the main road is closed for the winter, why in the world would any sane person think that a smaller forest road would be open?