Carts and discs can get worn too when not properly stored and handled.
For collectors this would be a problem. The game itself doesn't degrade in quality but....
Media definitely suffers from decreased perceived value over time, even if the disk itself stays pristine. A PSone game from 1999 will have lost more of its value (as a percentage) than a car from 1999.
And even short term it applies, otherwise no one would ever buy a game at full price at all.
Not saying the analogy is great, though.
Yeah games do suffer from a perception of quality over time. I don't believe devs see that as a logical conclusion though.
Honestly prices have to operate on Steam levels if they want to eliminate second hand sales. That would make more sense to me than a bizarre and complex half measure that keeps coming up in discussion. From a consumer's prospective it's far easier to either use the old system of used games or none at all but the pricing mechanisms will have to adjust.
And then there's the issue of how used products work in the EU and other countries. Steam supposedly was ordered to provide a system for reselling software but people tend to be happy with how things work so there isn't an uproar.
The whole thing is a cluster and Sony/MS need to clear this up. They honestly should have clarified it prior to E3 instead of potentially poisoning their entire expo.