Microsoft REALLY wants you use a Microsoft account over a Local account. The link to chose a Local account during install is gone. It only shows up if you get the Microsoft account login wrong, and there is no indication that a Local account is even possible until this happens.
We may never know for certain. But it would be weird if a backdoor in Windows could be disabled in such an easy fashion. It's not like the rest of the OS is fully transparent. I think a better analogy is probably using a Google account to log into a Chromebook. In both cases, you can look at the network traffic to see exactly the extent to which your computer is reporting on you.
Disclaimer: I work for Microsoft. Also, you can't imagine how confusing the term "Microsoft account" is for those of us who work here. That's why I still think of it as a "Windows Live account".
