Chicago real estate

I have noticed a recurring theme on this forum about how Chicago is the best urban bargain in the country, if not the world (For example, Chicago103 and Steely Dan both live in world-famous skyscrapers at great prices). Chicago seems to be an anomoly, a freak of nature. I am dying to know why this incredible city is do darn affordable when real-estate prices in so many lesser places are in the stratosphere.