Pheace: These days, PSN+ subscription = buildup of digital library with monthly free games, whether you're buying games or not. Over the long term you're still building up something you're not going to want to lose. It also means more and more console users are getting used to having games digitally as time passes.
Digital games on consoles is only going to grow.
Oh, I'm a PS+ subscriber alright, but I'm not as delusional as you seem to think. I know those games will disappear once my subscription ends, which is why I use it essentially as a rental service to discover games that I might otherwise not have touched.
I have on the odd occasion bought games on disc that I found great having discovered them through PS+.
The amount of stuff that I actually buy digitally on PS3/Vita/4 is very low, for the same reasons as on PC.