The reason for this is difficult to pin down. Perhaps the fact that people are out there running around in little more than underwear puts us on an equal basis. At roadraces, most conversations relate directly to running. However, the worn out ice breakers about work and weather are mercifully replaced with talk about mileage, injuries, the hills on the course, and splits. Post-race conversations easily cross potential boundary lines of age, pace, and every type of grouping imaginable, plus they always add a joyful dimension to an already satisfying day.
Runners inevitably become part of a unique sub-culture.
People are admitted without prejudice just because they run. There are no qualifications based on speed, age, or sex. Discussions about race are related to the one just run or the upcoming one. Peoples' socio-economic standing outside of running has no bearing on their status as runners. You are either a runner or you are not a runner.