If you search around under "power profile" i suspect you'll find a whole host of qualifications, not about the data used for that table but for how people (mis)use the that table.
FWIW, I prefer http://www.cyclingpeakssoftware.com/power411/profile.asp, as that way there's at least a smidgen of a chance that people will read the accompanying material...and even if they don't, at least it will always take them to the most recent version (#5 is currently waiting in the wings).