Perhaps the reasoning behind this thinking is that God made nature and people made buildings, ergo: Rural > Urban because there are more buildings and fewer trees in the city. They also might think that cities have lots of evil stuff: bars, strip clubs, universities teaching humanism and art galleries with naked pictures; whereas small towns just have food markets, one room school houses and, of course, churches. People in cities are too sophisticated for church but everyone in small towns goes to church.
Roger Finke and Rodney Stark's book "The Churching of America" says the theory of small towns being more churched than cities is hooey. What do you need for a church? If I'm not mistaken, people are necessary. And cities have more people than small towns. Big cities are more likely to have a variety of churches and often have a greater percentage of church attendees in their population.
More importantly, the Bible seems to take a different view of cities. Jesus spent time in small towns and the country, but He also spent time with the cities. He cared about cities. In Luke 19:41, Jesus weeps for Jerusalem upon approaching the city. Sure, Sodom and Gomorrah don't come out well in Scripture, but the first sin is in a garden, and the first murder is out on the farm. Heaven, on the other hand, is describe as a city -- the New Jerusalem.
God loves the city, and through the month of April, we'll be seeing what God is doing in four different churches in four different cities.