The American Heartland is making a comeback from a Rust Belt to a Tech Belt. It's shedding an image of FlyOver Land to FlyIN Land. Founders and their investors are discovering the industrial Midwest is the next frontier for innovation, and many cities from Pittsburgh to Columbus to Indianapolis are gaining rapidly. Still, a few rusted-out places are left behind. What is the difference between those cities on the incline and those that can't quite get up the hill.