To me, a good game isn't sold - it's kept for eternity. I love replaying games I enjoyed many times.
There are certain games that have a built-in reselling inhibitor. It's called
value. Look at Strategy games. How many copies of Civ 4 were sold back compared to the ones that were kept? There are people who still play the first Civ and say that it's never the same game twice. I myself still have Shogun Total War; I never sold it. Why? Because that game was so damn fun, and still is, and it has so much to offer in terms of gameplay. All of the Total War games will be mine for eternity, because of the immense value they have to me. The Simcity games; the Roller Coaster Tycoon games; the Galactic Civilization games; the Age of Empires games, etc - all keepers.
Great RPG's have that built in value as well. Show me one person who replayed Fable and I'll show you a thousand who replayed Baldur's Gate a dozen times. You can have my Copy of Planescape Torment when you pry it from my cold dead hands. Take a gander at how many people still play the Prophecies campaign from Guild Wars. There are too many to list in the RPG category.
First Person Shooters? Take a look how many people are still playing Counterstrike, Unreal Tournament, Quake 3, Operation Flashpoint, Deus Ex, Thief and others. It's the value these games offer after the first run through that keep people from getting rid of them long after there are newer alternatives on the market.
I haven't even mentioned the biggest value-add in PC Gaming - the modification. When you bought the original Half-Life, you were actually buying about 50 different games because of the huge array of diverse, awesome mods out there. There is still an entire community of people making missions for the original Thief and Thief 2. And they are fantastic. If you are at all a stealth shooter fan, trust me; do yourself a huge favor and check out the fan made missions for thief. Calendra's Legacy for Thief 2 is the best mod I have ever played and is way better than a hundred games I paid 50 bucks for.
I laugh when developers whine and cry about not getting a piece of the pie in the used games arena. Sorry, fellas; capitalism and a free market doesn't work that way. Perhaps if the average game today was more than what amounts to a day's worth of disposable entertainment, your piece would be much bigger.
“The greatness of a nation and its moral progress can be judged by the way its animals are treated.”
- Mahatma Gandhi