I simply don't believe that people go into a PC store to buy a Windows PC and come out with a tablet - regardless of the OS on it. You simply don't want a tablet if you went in to buy a laptop, and you simply don't want a laptop if you went in for a tablet.
The data doesn't show that people aren't buying Windows8. It shows that people aren't buying PCs. It's not hard to buy a laptop with Windows7 on it either - so suggesting that the decline is "because Windows8 is turning people away" seems to be cherry picking the data somewhat.
The fact is that laptop and desktop machines have seen a dramatic fall and are forecast to continue falling in sales since long before Windows8 was on the market:
So how do you, as CEO of Microsoft in 2010, adapt to the challenge of your entire market disappearing in front of your eyes - you're winning the Enterprise market with Windows7, and that's great, but the consumer market for PCs is rapidly vanishing and you know that once it's gone, Enterprise will follow it.
The answer is you adapt your OS to consumer needs. You need your OS to focus on being effective and usable to how customers clearly want to interact with their device: They want their device to be small, touch-sensitive and to be able to install apps. That's what the success of Android is, it's what the success of iPhone is, and it's something that Windows7 clearly doesn't do well.
So what do you do?
You make Windows8.
Windows8 is not about making people use tablets, or forcing people to use applications and touch-screens. Microsoft doesn't really care all that much about what hardware you use. It's about being able to work on tablets so that they are still relevant when you stop buying laptops, and being able to use touch-screens (since tablet + mouse = suck) and run apps, since that's how consumers increasingly like to interact with rich applications.
That's not to say consumers don't want fully featured applications on the desktop or mouse support or laptops. And that's why Windows8 didn't drop support for any of those.
That way you're protected against the market for PCs vanishing and Windows vanishing with it. If the market for tablets goes away and people get bored of apps, Windows8 is in a strong position to head back to Windows7-land of desktop applications.
If on the other hand the analysts are right and customers continue to vote with their wallet to move to apps and tablets, Microsoft will have a strong and reasonably familiar product in the market, and will hopefully be a strong player in the market by the time V2 and V3 come out before the crash in the laptop/desktop market gets to crisis point for Microsoft.