It looks like this count is coming from someone monitoring what OSs they see in use. That being the case, it must be greatly under-counting Windows 8 and Win 8.1, since while they may be on many more computers, they are unusable.

8.1 might be a huge step up, but it doesn't matter. People remember the UI disaster that was Windows 8, and figure 8.1 can't be that much different. It has such a bad reputation, they'll need to call it something else to sell it at this point. Would you even consider having a doctor give you Cancer.1, or would you hear the question and immediately get yourself a new doctor without even finding out what Cancer.1 was?