The 15-Year Rule

It's been a while since I've been out actively looking for random videogame stuff, but as the summer thrift and rummage sale season kicks in I'm trying to hone my deal-searching radar again.  One thing I'm noticing is that, in my first such round of activity back in the mid-90s, I found a lot of stuff from the early 1980s.  It wasn't unusual to find troves of Atari 2600 and Colecovision games at that time, in middling, shoebox-stored condition, but they were there.

Today, in 2011, the window seems to have shifted, but the time lag is similar.  Now I'm mostly finding stuff from the mid-1990s, with a lot of Playstation and Nintendo 64 hardware and games in the mix.

I wonder what drives this apparent fifteen-year window -- yes, I know I only have the two data points, and it would be more realistic to call it a fifteen-to-twenty-year window, but bear with me here.  Is this time period a generation, roughly?  Get a system when you're a kid, be ready to part with it as you're becoming an adult?  Is fifteen years an average threshold of sorts for family moves, when unused stuff in the closet gets jettisoned?  Is it when youngsters are setting up house and Mom and Dad start to send them all the junk they left behind when they went to college?

Mysteries of the video game universe.