It's not just games for me - it's movies, old magazines, and especially books (I take after my dad - our collection of books we've amassed over the years would put most libraries to shame). It's just that everything has some emotional value for me and it just doesn't feel right to trade it away. About the only exceptions are games that I just know I will never, ever play again - and then I prefer to give them away than trade'em in.
Now it's even easier - I just don't have as much time for gaming as I used to, so I get a new game every 3 months at the very least and it takes me a looooong time to finish one. And then, I like to go back to my old games every now and then (I don't think there's been a single month in the past decade when I didn't play "Baldur's Gate" for at least a weekend).