Going back to the original findings, they don't appear to match what the NSAA has found. http://www.nsaa.org/nsaa/press/historical-visits.pdf
Looking at those figures, the total numbers appear to hover between 50-60 million, with obvious peaks and troughs that coincide with snow totals and the economy. So, although the number of people who have skied at least one day might have decreased, the number of ski days logged has remained relatively constant.
If you want a full report of total figures, this is pretty good http://www.vanat.ch/RM-world-report-2011.pdf. (The author really needed a native editor to smooth out the language, but the statistics are brilliant.) This report even states that the number of skiers in the US is up over the last 10 years.
That was interesting. A couple of things: "Austria is also the only country where the schools are still going on ski weeks on a systematic basis. This may