" ...Basically Windows XP and Vista users were enticed into trying out the "Insider Preview" version of Windows 10 to help Microsoft find bugs and react to feedback. ...
As a reward for their input into Windows 10, the "Insider Preview" users were to be given a free upgrade to the full version when it has been fully released.
Except of course now they aren't. Microsoft has changed the terms. Only Windows 7 and Windows 8 users will receive a free upgrade to Windows 10. "