If you look at the map I linked to above( let me link it below again) you would see what Sprint means by Chicago. By Chicago they mean Chicago land. They're listing specific cities in press releases to show that they're making progress throughout the market. I think when people living around the city of Chicago hear that Chicago is getting LTE they expect it to include Chicago land.
Here's Sprint's LTE coverage
and AT&T's LTE coverage
Sprint covers just as much or more of Chicagoland than Sprint and in every market they're deploying in their LTE coverage goes further out of the city's boarders.