About 40% of games hang around longer than 2 years. I think I'm doing fairly well to stand against the incoming tide of new games, holding onto the good stuff (as shown by the bottom of the graph being greenish) and dumping the stuff I don't like (as show by the top of the graph being pinkish).
The factor that stops games being played for longer is, as always, the fact that I have way too many games and not enough time to play them all. This is not necessarily a sign of shopping addiction on my part though, it's more a case of drinking from a fire hose with only a port glass to hold water in. I think if I can identify great games and continue refining my collection, I'm doing the best I can. Also, if great designers would stop designing great games, that would help.