Trust in NetMarketShare
NetMarketShare's Vincent Vizzaccaro tweeted about ZDNet's errors in comparing operating system numbers provided by NetMarketShare and how they corrected them:
A closer look at those Windows 8 and Windows RT usage numbers www.zdnet.com
Besides this there's also another issue which was neglected in this article: Why isn't NetMarketShare able to provide numbers which allowed correct comparisons? Assuming that they have the raw data that the numbers they publish is based on, they could easily compare those.
Furthermore they say that Windows RT's listing in the market share stats was an error and should not have been there in the first place. Windows RT stats are being included in the Windows 8 numbers. From Microsoft's POV it makes sense to only have Windows 8 numbers but in reality those are two completely different operating system - where completely means: apps developed for one don't run on the other and one is a stripped down version of Windows 8 optimized for tablets and the other one is a full desktop operating system. NetMarketShare differentiates between iOS and Mac OSX then why not also between Windows RT and Windows 8?