I think that the problem is that people seek pleasure rather than joy in life. We become desensitized to things that are pleasurable but when we feel joy from love, helping someone, expressing ourself a creatively, etc. that kind of happiness never gets old.
I have a friend who lives a very high life style. He gets a new Porshe every few years and recently at a group morning coffee he was talking about getting his wife a new car when the car she has is very nice. When he was done talking about his upcoming car purchase I started a new conversation about our cars being almost 10 and almost 20 years old and how wonderful it was having older things that still provide great service. I think my buddy needs to feel superior to people who don't have as high a life style. The funny thing is that I have way more economic resources than my friend.
I liked Seth's point that in a networked world where things can be shared that we lose the feeling of exclusivity, which I think is a good thing!