Missing the point, remember my other job deals with this.
Software licensing and Software ownership are two different things.
Most software licenses say that you can not sublicense or simultaneously use one license of a product, when the value of the game 'license' is the key and not the physical media or installation medium (I can buy the media for adobe anything for 25$ from adobe, but the key still costs hundreds to thousands of dollars.) This is especially the case with Microsoft, the creator of the "software license", in which not only software can not be resold, but you can not sell the software that came with the machine, even if you never powered it on. (You see a lot of people trying to sell vista, who have dowgraded to XP)
Because games that can be played multiplayer version check each other, it's difficult to for such software to be pirated or modified to bypass the key, since it will block you from playing multiplayer with others. This is the case with all Xbox360 games.
Have you noticed that you do not need a 'key' to play console games? In those cases, the value is in the physical media, however the same license agreement applies. You can resell console games, since pirate copies will not work on other unmodified consoles, nor can you copy the game yourself without special knowledge. Did you know that Nintendo software comes with keys for you to register? (Warranty purposes) If you acquire a new or used game from India, maylasia, singapore or hong kong/china or taiwan you are more likely to get a professionally counterfeited software?
Used DVD's have this special grey zone, where people buy or rent them, rip them to their media server, and then return or resell them. There is no 'software license' for dvd's, it's media ownership only. You are licensed only to view it in your own home, and fair use dictates you can make a backup copy. You are safe untill you try to distribute it (eg, give the disc back to the store or resell it.) However there is a lot of counterfeit software out there, particularly showing up on online sites like including trusted sites like amazon.com from third party sellers. Counterfeiters usually go after box sets however.
So going back to the original posters example. Used software has, and always has been "no return", since it can be copied/installed and then returned. It physically has to be defective, and if it is, they only exchange it for the same software. If you bought a used copy of software, you should be aware that the media itself is the only thing you are getting, not the license. (See my adobe reference.)
As a general rule, for software, if someone is selling it for less than you can buy it from the companies online store, it's a questionably licensed copy.
http://www.theesa.com/policy/antipiracy_faq.asp and
http://www.bsacybersafety.com/protectin ... tduped.cfm
If you try to sell Valve software on eBay (including the steam account,) Valve will tell eBay to remove it for software licensing issues.