My theory is clutch life is inversely proportional to the number of traffic jams encountered. And left leg strength is directly proportional to same...
Never replaced a clutch yet, all my cars have gone over 100K even with spirited driving. In my high school set, it was a point of religion to keep your foot off the clutch and hand off the knob when not shifting... people would call you on it. I think that discipline helps with long clutch and tranny life.