If you buy the box software, you can use the software anytime thereafter so long as there is a hardware that will support it. But if you subscribe and terminate the subscription, then you lose the use of any psd file forever.
And to be fair, each time you buy a new camera you willingly pay for a new version of Photoshop, even if you don't need the new features? Just looking for support for new camera, not new feature. And by buying box software one can skip generation, not constant upgrade.
But my biggest grouse is still I will lose my psd the moment I stop paying. Or when I am hiking in some remote place and the computer cannot access the internet...