People have 30 days to decide and thats what ( obviously) their doing.
50% of all statistics are just made up.
My upgrade to Win7 those many long years ago was free. I wasn't interested in 8 so it didn't matter. The free upgrade certainly got people to upgrade sooner rather than later. I would have upgraded, even if I had to pay for it, just not as soon as I did. For those whose Win10 is stable, they will be content and few will revert back to a previous version. In much easier to use on a desktop than 8, and works as well as or better than 7. Once the 3rd party drivers are sorted it will be the OS of choice for normal users. There will always be holdouts, and those that have special reasons to stay with whatever version they have, but for most 10 will be just fine, either as an upgrade or on that new machine they're going buy.
In reality, at least I admit I have no information one way or another, and that it's my personal observation/guess/thought that people are not deciding to "keep Windows 10 or not"...unless perhaps they have difficulties with it, and roll back to the previous 7/8.1 version.
I have no numbers either way.
And quite frankly, I have absolutely nothing invested in the future success or failure of W10.
I like it on my system, but don't give a fig if 75 million people shout "holy crap, this sucks, get me back to my previous OS!" or "Someone help me put Linux on this thing!" or...you get the idea.