A game shouldn't lose it's value just because a single year or two has passed. There are still sales for the game here and there, although they're retailer specific.
I say this as someone who aims to get into software development, and dislikes the race to the bottom much of entertainment software in different industries has reached. I even look at Steam, and see more and more indie developers releasing games at $15 and sticking to it unless it's one of the crazy Steam sales that happen twice a year now (analogous to Black Friday) or they're participating in a Humble Bundle. Software has a value, and it should take many years and better software that forces the value of older software down.