Why do these systems need network access to play a game bought on a disk? That is the bigger question, sure I can understand only supporting multiplayer through a centralized service, my issue is with the activation and phone home crap. There is no "good" reason someone should not be able to use these things without network access for single player experiences.
Customers out realize that the system is brittle because Sony and Microsft created a hard dependency where there never needed to be one. It might not be their fault they are attacked, but they do know or should have know they are targets. Hopefully the lession they take away from this is that basic functionality should be there if you have the system and game disk fresh out of box. Maybe you can't update, download new content, do multiplayer but folks ought to be able to at least play with it even if the network is down.
I can't speak for MS and the Xbox, but I managed to score a free PS4 at a work holiday party and there are only two games I have on disc that have been unplayable during this outage, Plants Vs. Zombies Garden Warfare (the game has an 'offline' mode that should be accessible when the network is down, but apparently not) and Destiny (on-line is kind of the whole point of the game, so at least understandable that it doesn't work). Everything else I own, even the stuff that was acquired digitally and downloaded straight to HDD works just fine.
So yeah, Sony did not create a hard dependency where there never needed to be one. During the outage the system has been playable, the majority of the games have been playable, disc or not. Instead of playing Destiny, I played Samurai Warriors 4. Aside from not being able to play on-line games, the only real difficulty I could see someone having is with a new console needing an update in order to play some newer games as I'm not sure if there is a work around for that. In the past I've seen companies ship games with console updates on disc, not sure if that practice still happens.