Lots of the trends are affected by video game industry factors, and some are affected by factors from other realms. It would seem like the dip since 2008 may be economy related. The recession of 2008 didn't help things on a global scale, and of course it didn't happen too close to gen start, so gen start couldn't offset it I'm thinking.
http://en.wikipedia.org/wiki/Late-2000s_recession
Hey Seth, do you have a source, I'm trying to maintain a list.