Once you purchase it your account is granted a digital license for that game.
The name of this article is "New patch reportedly makes Silent Hill P.T Unplayable". New and official patch that makes your game unplayable. Nevermind the fact that's a demo. If the precedent is set they will allow this things to happen by just adding that condition to the agreeing license noone reads.
This is different because at that point you've purchased a product and now Sony has purposely made it unusable. At that point the console makers would be opening themselves up to lawsuits. They can do this with PT because it's free and was never sold by Sony for money.
Honestly if you want to get an idea of what digital only gaming looks like just look at Steam. It's great I've been using it for years no issues ever. Console makers will just follow their lead they wont do things like make games that people purchased unplayable on purpose because not only is there no reason to do that but it will also open them up to lawsuits.
I'm pretty sure they can just loophole their way out of that problem. If they really want to, they can just change the definition of "digital purchase" so that they can just say it's an overglorified rental and force you to buy it again after 5-10 years. And by that point, the game might not be on sale at all... Everyone wants entertainment in general to go the way of Netflix, after all, so buying games might not be as good as subscriptions for their games, at which point they can add or substract games as they please, who is going to stop them? You didn't buy the game, it's not yours.
And also, for most of games they wouldn't even need to be that crafty. Just imagine how many mp-only games are going to become obsolete on consoles once the servers are down, without the need of subterfuge.