Hi Folks. That is indeed beautiful step mountaineering skiing. I'm familiar with the area and have climbed around there lots of times. The conventional approach would be to take the lift up to Grands Montets, skin up the glacier, spend a night at the Argentiere refuge, and then climb the face, before skiing down (also very possible that they did it in one push, i.e. up and down in one day). Coming in from the backside would be a much longer undertaking, and my understanding of these steep lines is that the skiers nearly alwasy climb the route first, to check out the condition and the line, before skiing down.
In terms of the climb, that's an accomplishment itself. Their climb up, for example, the Swiss route, that they partially descended, is a 50-55 degree sustained alpine climb. They would likely be using two ice axes, crampons, perhaps roping up a pitch or two, although these guys are so skilled they could easily solo or simul solo the whole thing--unless they climbed a harder more technical route on the face, which is also possible. I've climbed routes like that (though not quite as long, and when possible I definitely like a rope and rock rock or ice protection when possible! It always amazes me how these steep skiers ski down what for me would be an awesome adventure just to climb up!
In terms of skiing...steep skiing like this seems to be almost like a sport unto itself. I do some basic ski mountaineering, but absolutely nothing like that. I think steep skiing of that kind is one of the most dangerous games you can play in the mountains--and probably also amazing and exhilarating. One assumes that they have an absolutely solid foundation in all aspects of skiing, and I think that's fair. The IMGFA ski tests for high mountain guides are notoriously difficult to pass. That said, guides around Chamonix might spend 100 or more days on skis a year, and hardly ever go on piste. I would guess that their styles and skills are very different from, for example, a high level piste ski instructor (not better or worse just different).
The skilled skiers around Cham who are skiing these steep lines are certainly pushing the limits of the sport and what is possible. Here's a typical example:
There seems to be one young skier who can actually ski these steep faces with broad smooth linked turns--people talk abut him as a phenomenon, taking steep skiing in a new direction, somebody who makes skiing these faces look like skiing on piste. A recent movie of his has circulated widely. Hard to remember when watching the movie how steep those faces actually are:
http://www.laliste-film.com/
Nearly any one of the faces he skis down would be a big goal for me to simply climb up!
Enjoy and be awed.