I see your point, however the presence of used games ALWAYS provides a cheaper alternative. The price point is irrelevant. If new games were $10 and used were $8, people would still buy used, in the same way that pirates still pirate games which are on sale for "whatever you want to pay", or as little as a single cent. They still pirate, because it's cheaper.
Making it easy for used game buyers is not a good business model for the pubs or devs.
As a follow up on this topic, I believe we wont need discs much longer.. its really an outdated form. Eventually we will be able to just download any game we want from the internet and store it on a hard drive for use. I mean when is the last time you actually bought a music CD? That cures most of the piracy problems and used game market.... I would imagine the longer a new game is available as a download the more the free market will take over reducing the price similar to what a gamestop does. I understand music and games are two different monsters, but eventually thats where we are heading IMO, bad news for the gamestops and blockbuster videos of the world.