I don't know of anyone who disagrees that there are fairly strong differences between Urban and Rural life. The needs of individuals within those areas are totally different. It's no wonder, with our political system, that parties would, to differentiate themselves, attempt to reach individuals within one group or another. (Or hell, likeminded individuals could form together into a group.)
Indeed, what's really interesting is that this is somehow seen as a NEW development. People have pointed out Republicans were originally seen as in control of the northern states, Democrats in charge of the southern states during the Civil War. (ahem, or War of Northern Aggression as some people have pointed out. :-) Obviously there were incredible differences in the cultures of North and South - from lifestyles, to resources, to industry.
It's also interesting that the nature of the parties have changed over time. Originally, Republican were seen as in control in the North, particularly in the Northeast. However, as time has progressed, the party now is seen in hold particular power in the midwest farmland and in the south. The urban control (particularly in the Northeast) that it once had is now seen to be held by Democrats. I suspect that this may be influenced from the Reconstrution itself, as Democrats were forced (as a party) to reach out to anyone (immigrants in particular) to retain power (however, I could be wrong).