Maybe people from other cities can shed light on how unique of an issue this is, but basically Chicagoans have an irrational and extreme attachment to long-gone Chicago stores and products.

Examples of this include:

• Frango mints
• Marshall Field's

Evidence

• "Why are people still so upset about Marshall Fields?"
• "controversial and very public protests from former Marshall Field's customers and Chicago Mayor Daley"...to moving production of Frango mints out of Chicago. [from Wikipedia]
• When Marshall Field's was going to be renamed to Macy's: "The announcement aroused widespread anger across Chicago" [source] Note: priceless for inclusion of a sampling of wrathful tweets in response to this issue.
• Just read this.