I'd argue that the only case where you need a subscription model to stay afloat is when you don't add enough value that your users will be willing to purchase a

I'd argue that the only case where you need a subscription model to stay afloat is when you don't add enough value that your users will be willing to purchase an upgrade. Windows obviously provides a good amount of value, but big upgrades are undermined by the need & expectation for ongoing regular updates, which means <Prior Version Latest Patch> is usually significantly better than <Prior Version RTM>