On Windows 7, you didn't have to have Flash installed. Windows 8 was, I think, the same.
On Windows 10, on the other hand, it came bundled with the system and wouldn't let you remove it*. A strange decision and I really have no idea why they did that. Better late than never, I suppose, but it's Microsoft's habit - never fix a bug until users have been screaming about it for eighteen months.
* Various workarounds existed, but they usually either broke Windows Update in some way or another, or made it nag you forever, which is more or less the same thing in my book.