Not THE reason; there are a number of reasons why my partner and I are moving to Portland.
But I've been using this illustration to explain one of the prime motivators behind the move.
In a lot of video games - for example, World of Warcraft - there are "zones" where you do quests, gaining levels and experience, and then you move on to the next zone. I kind of feel like I've leveled past Tulsa, that I'm done with Tulsa, and it's time to move on to a new zone.
A geeky explanation, to be sure. But then, I'm a geek. Actually I'm a gork - a geek/dork hybrid, but my point stands.