I can equally name a bunch of other cities with similarly well-positioned academic instituions. That doesn't make it unique. For example, look at the Research Triangle Park area in North Carolina. Not one, or two, but at least three or four major world-class institutions: Duke, UNC, NC State, Wake Forest, and others. With tons of research and supporting institutions. And a cost of living very comparable to Pittsburgh.
Or how about Philadelphia with Penn, Temple, Drexel, and more? Or Baltimore with Johns Hopkins? And of course, Boston with its concentration of dozens of the top-rated schools in the world (Harvard, MIT, Tufts, BU, BC, and on and on).
So in what way is Pittsburgh unique? It's not -- it's just like many of these former rust-belt cities with world-class institutions and a startup economy that's interesting but not on top.