They start building little markets out to pump their market count up. AT&T and Verizon didn't do that- they tackled NYC, SF, LA, Chicago, Boston, etc, etc, right up front where LTE is actually needed (Ok, Sprint's 3G is so bad that everywhere needs LTE, but still...).
The small cities aren't markets, they're cities in larger markets. Chicago encompasses all of what most people consider Chicagoland. Chicagoland has over 1000 cell towers alone which take several weeks to completely upgrade from start to finish. By announcing these cities as having LTE they're saying/showing that they're making progress in the larger markets.
Sprint works from the outside of the market inwards in most cases. I'm assuming this is because they want to bring the upgrades to the people first and provide a network that doesn't cut off once you leave a major city's limits.
Look at both of these maps I have linked to below and tell me which has more coverage in markets where LTE is/has been deployed.
No... AT&T are missing huge chunks of LTE coverage.
Those maps are generated by users using the Sensorly Android application which reports what your phone is connected to along with the GPS coordinates to create an accurate coverage map. Enough people use the Sensorly application to provide an accurate representation of actual coverage.
If you know it exists and you're going to be traveling through that area go ahead and download Sensorly and map the area. Sensorly uses crowed sourced data, it's not going to show what hasn't been physically mapped. But it certainly does give a pretty accurate representation of coverage in places people frequent.