I've worked hard for the past 10 years to get to my middling-middle class income. Enough with my wife's to support our family. I could just be content with that and staying right here for the rest of my life, never wanting to do any more with myself, but I know things will change and i want to be prepared for it.
Maybe it's the brain wiring of a software developer, but I refuse to become complacent with where I am at. I already know I wouldn't last another 10 years if I don't regularly adapt, learn new technologies, stay current.
I think in a way, this isn't too much different than the housing bubble. Too many people thinking that everything is just going to keep going its steady pace forever and if anything bad does happen, someone will come to the rescue. I want to position myself so I don't need that rescuing.