What would be peoples motivation to buy it for existing computer?
* "It's sorta legal, it's at least some kind of a licence, right?" -- they're misinformed / tricked /fools
* "I want to pay something, but retail costs too much" -- if you pay without getting anything useful in return, you're donating. Why not donate to charity?
* "I want to get Windows Updates" -- cracked copies used to get updates, and they're often bundled with updates already applied
My point is, I don't understand buying half-valid licence. Licence is either valid or you have no licence.