For me, this is not true.
I only buy the games I want to play completely through. I don't buy them for the shear thrill of having them in my collection. Altough I do consider myself a collector of great RPG games.
What I do is buy a game, play through it, put it away buy another game, play through it, and so on. If i have more than one game to play I play a little of bothm but eventually get hooked on one, beat that, and then move on to the other. And most games (mostly RPG's) that i beat, I don't come back to for quite some time, as I am always playing a new purchased game.
Also, I try not to be playing more than one game per system, so that I can avoid being unable to decide what to play.

Also: I agree with Gideon, I think being older has a lot to do with it. When we were all kids what did we do? Got to school, come home, tell our parents we didn't have homework (well atleast some...including myself)....and why? So that we could play video games all through the evening up til sleep time. And weekends, were like holidays dedicated to playing video games.
Now that I am older, (and I'm sure I speak for a lot of other people here) I find myself playing less. Here are a few reasons:
1.) Wife/Girlfriend
2.) Kids
3.) Job
4.) Spending time with wife and kids (Dates/Vacation/Outings)
5.) Much more responsibilty and things to care about and work on
6.) I would say a general loss of interest, people realize as they are older that there are more important things to spend your time on
7.) Rules 2, 5, and 6 do not apply to me.