It isn't that it isn't integral - in fact, I see it as integral enough that I truly think Chicago keeps the midwest alive, at least portions of it. It is just different. A lot of the problems that other midwestern cities have - decline of factories, for example - chicago is able to make up for to an extent. And to me, that is the main thing: The chicago experience doesn't match the average Midwestern city experience - and discussing chicago directly takes a bit of time. Hence the exclusion in the article.