So, basically, they're measuring the length of every run and then adding them up? That's sort of crazy for here in the West because so much of our skiing is open bowls or, here in Whitefish, trees. Are they only counting groomers? Again nuts. Most of the "more desirable" terrain here is NOT GROOMED. In fact, on a powder day, you'd cause a riot if you started grooming some areas. Basically, here, if you were comparing total groomer length you'd be destroying reputations.
Yes, the standard over there is measuring the resort in terms of 'length' and not area like they do in the US. At a lot of European resorts, once you are off the groomed trails you are "out of bounds" in terms of avi control and rescue -- sometimes even if you're just on an ungroomed hillside between two groomed trails! They may be prohibited from advertising such terrain as being part of the resort.
Also, a lot of the larger resorts are above treeline (and the trees that are there tend to be much denser than in the Western US), so my impression is that glade skiing is not as big in many areas.
Ski areas exaggerate (period!). Just have a look at Jay Peak snow fall reports, if you do not believe me. They get good snow, but there is no way they get twice the snow fall of nearby Sutton or Burke.
While I have not made it up to Jay, people I know say they do get some weird microclimate things that can cause them to get more snow than the surrounding area. I dunno about twice as much, but I wouldn't be surprised if they got significantly more snow than some other resorts in the area.
There is a more extreme example in Salt Lake City. The Cottonwood Canyons resorts (Alta/Snowbird, Solitude, Brighton) are not actually very far from Park City as the crow flies, but they get WAY more snow. The shape of the mountains and the prevailing winds cause the storms to dump substantially more moisture on the western side of the Wasatch (SLC) than the eastern side (PC). So this sort of thing can happen.