I see, you're right that PS3 doesn't need any internet activation for the games. However (to play devil's advocate slightly), that doesn't mean Sony can't easily shut off your game; the internet isn't the problem. Sony can issue a patch anytime that turns off features or blocks certain games, and Sony can also make that patch a pre-requisite to playing any future games (this point is mooted by the fact that the PS3 probably doesn't have any future games, but it applies equally to the PS4 or any device for that matter).
Remember what they did to OtherOS on PS3? They can do it to any software, anytime. So you could keep two PS3s around, one pre-patch and one post-patch, to play the respective games. But thats not really efficient; not any more efficient than worrying about steam servers being shut down. Plus, what if they issue 3, 5, 50, n patches. Will you keep n PS3s around for full compatibility? My point is that physical media isn't necessarily more secure or exempt from external control. Personally, I have more faith that Valve won't screw me out of my Half-Life purchase than faith that Sony won't screw me out of using my PS3 the way they promised on the day it was released.
Also, I think the internet helps keep games around forever, it doesn't hurt that. The internet facilitates more freedom to play games than any console ever. I think eventually all good games will become available free online, in some form. Either through abandonware, expired copyright, or fair use. It's already happened to plenty of games (
https://archive.org/details/software). Keeping a PS3 around for 20 years is silly; that would be like keeping my Intel 80386 computer around so that I could play King's Quest today. It's easier to just fire up DOSBox on whatever I have.
As an aside, I totally still rock the Dreamcast sometimes... emulated of course
