Note that the report you link is not really correct; I know I (and many other power users) set my Windows Mobile to report as IE7, so I'm not shuttled off to some limited mobile web version of a site (99% of all sites are perfectly fine in Opera and PIE). Meaning that there are plenty of WinMo users who don't show up in that list because we don't report ourselves as limited browser.
Same thing for iPhone. There is no reason to go to the crippled mobile websites when your browser is fully capable of seeing the full site (albeit, minus the Flash content.). However, I do not believe that NetApplication's OS scanner uses the browser to determine the visiting machine. NA has a separate report on browser statistics.
I do take issue with NetApplication's new statistical model of imputing (guessing) additional Windows usage for non-polled nations, such as China, and adding it to their figures, which they started doing in February, assuming numbers not truly in evidence. . .
I would, however, point out that we power users who so change the setting to spoof the readings of the polling sites like that are a drop in the proverbial statistical bucket and would not skew the demographic an iota. We simply are not that numerous.