I didn't notice at first, and really, there's no reason why I should have noticed. Also, I assumed Windows 10 Home didn't come with BitLocker anyway.
The Windows 10 security overview on Microsoft TechNet includes the following statements:
"Modern Windows devices are increasingly protected with device encryption out of the box and support SSO to seamlessly protect the BitLocker encryption keys from cold boot attacks."
"BitLocker supports encrypted hard drives with onboard encryption hardware built in, which allows administrators to use the familiar BitLocker administrative tools to manage them."
https://technet.microsoft.com/en-us/library/mt601297%28v=vs....
Apparently it's "device encryption" but it's not BitLocker. And while it's optional at the moment, it becomes compulsory in summer 2016.
Unless you have a Home edition of windows, in which case you have no control over it at all. In order to use device encryption you have to sign on with a Microsoft Account and Microsoft will have the key.