Why would I want to pay a subscription fee? They're not providing a service, they're selling a product. I don't want something I don't actually own running my computers.
WGA is program to detect if their is a valid key or not installed on the system and can take different actions based on what it is. There is a proof of concept built into Windows 8.1 as if you've noticed, the product keys for that and Windows 8 are different. If WGA had detected your Windows 8 key was invalid, it wouldn't let you install Windows 8.1 at all. If it was, the Store issued you a brand new key.
I suspect that if WGA detects a bad key (or none at all) for Windows 7/8/8.1 to Windows 10, it will reset it back into the 30 day grace mode and not issue a key (which is actually standard for Windows installations as a fresh install is legit for the initial 30 days regardless of whether you have a key or not).
[Edited by Neo7, 3/20/2015 7:53:50 AM]
I never said anything about you, or anyone else, having to pay subscription fees for Windows. I said I would like for that to happen because not everyone has west world's salaries and can afford to pay $500 or $1000 for a simple, 5-use, Windows disc/key.
I'm already paying $30 a year for my AV software and I have no issues paying $50-60 a year for an OS.
And as Neo7 explained right under your post, even if you buy Windows you still don't own them. You merely paid for the privilege to use the OS.
P.S. Apologies for going off-topic.
[Edited by LordVenator, 3/20/2015 2:31:02 PM]