Looks like the footnotes from that page lead to the book "Invisible Engines: How Software Platforms Drive Innovation and Transform Industries" for the 17m figure.
http://www.26econ.com/pdf/InvisibleEngines.pdf
So I downloaded the book from MIT press, and then find that the book got its 17m figure from a Dec 2000 Cahners In-Stat report at the time of the original X-Box's debut. A copy of the Cahners In-Stat report in .pdf form costs $2,495.
http://www.mindbranch.com/catalog/print_product_page.jsp?code=R97-575
Screw that! GamePro says the Saturn sold 9.5M, I'll trust GamePro! :p
http://www.gamepro.com/article/features/111822/the-10-worst-selling-consoles-of-all-time/
FWIW, the Invisible Engines book also notes the original PS sold nearly 10m in the first two years, but then exploded to hit 26m total in year three. It achieved 81m after year six, for those wondering about original PS figures.
