Agence France-Presse (AFP) caused quite a stir when it reported Steve Ballmer saying that Windows 8 would have up to 500 million users by the end of 2013. But Microsoft says that Ballmer never made that prediction, and the AFP article was based on a misunderstanding.
A Microsoft spokesperson contacted me to say that "the stat Ballmer gave was actually a restatement of the same data already announced in December at the [Windows] Store event regarding the number of Windows 7 devices that could potentially upgrade to Windows 8 -- so there's no new data here. This was actually just a case of some confusion in terms of wording."
In other words, Microsoft says that the 500 million figure Ballmer gave doesn't refer to the number of copies of Windows 8 Microsoft expects to sell. Rather, it's the number of Windows 7 licenses sold, each of which could be upgraded to Windows 8.
Microsoft says that Ballmer was just restating what Ted Dworkin, Partner Program Manager for the Store, wrote in a blog post at the time of the Windows Store event:
"We've just passed the 500 million licenses sold mark for Windows 7, which represents half a billion PCs that could be upgraded to Windows 8 on the day it ships. That represents the single biggest platform opportunity available to developers."
Not having been at the event covered by the AFP, the Seoul Digital Forum in South Korea, I can't vouch for what exactly Ballmer said. But in fairness, I thought you should hear Microsoft's side of the story.