High cadence (100 rpm and higher) cycling is great for developing a nice pedal stroke and improving the strength of your aerobic engine. Low cadence (50-60 rpm) cycling, against a big resistance, is great for developing muscular endurance and cycling-specific power.
This right here is all you need to know.
As a former personal trainer I find it safe to assume that everybody's genetics varies to a certain extent. To explain further, everybody has a different level of muscular strength versus cardiovascular endurance. While the two do correlate to a certain degree, it is clear that for some people, (like me) pedalling at a relatively low cadence (note, I'm not always pedaling below 70rpm) works best according to the efficiency as well as endurance of their nervous system.