Re: just a thought....
I like a and c. Over the years, I've come to believe the os version does not sell the computer. The os only matters to the degree that the user's applications may continue to run.
Here's a loose proof. Microsoft has telegraphed its release of the next Windows versions 12-24 months in advance. If there was a wait-for-it phenomenon, Microsoft's ears would be scorched by the language the OEMs—Microsoft's true customesr— would use on the phones and in memos every month that release didn't follow pre-announcement. Also, Vista, Win7, and Win8, according to some circles, were likely to boost pc sales growth, but I don't think the effect, if any, could be shown to be significant.
Still, in June/July 2012, we had Win8 on the way, less employment (I write from the USA), and summer was still summer. Did we see a diminishment of the fall-off in XP and a flattening of Win7? I don't recall as we did, though to be honest, while these usage stats do arrive monthly, the reporting on them is a tad scattered as writers cherry-pick moments in order to the use the snapshot, rather than the trend, in order to make some case that Microsoft has [the mojo | the curse] with regards to a new or old os.
The key points, and these have been clear for a few months, Win8 is not growing as fast as it should (and most of the causation goes to the pc market) and XP is not declining as fast as it should—from Microsoft's perspective, of course. If one is using XP securely, well, why care that Microsoft thinks it really, really important that one gives it a couple of hundred dollars for a new os and half a day towards reinstalling applications, tracking down license keys, sorting through activations, etc., all done with some risk that key applications from minor or aggressive vendors do not run on the new shiny, now with Start button restored (!!!!! - LIstening!), as soon as it's released, any day now, no really.