BRRR!!! -40 and skiing doesn't sound like fun. In my opinion, skiing stops being fun somewhere around 0F (somewhere in the range -15-20C). The shoes are simply not warm enough (unless you use dedicated "expedition boots"). Keeping your feet warm is the single most complicated issue when skiing in very cold weather.

I haven't done much snow shoeing, but my impression is that the bindings leave much more flexibility for you to use whatever boots you like, including those that are rated -40C or colder.

According to the article, this group had no exceptional trouble except having to walk throughout the night to return to their cabin. It simply was too cold for them and their equipment to stay outdoors that long.