Gearbox oil doesn't get dirty and contaminated like engine oil, they probably set a reasonable life for it to cover all conditions, but I doubt going over mileage would cause failure of anything. I don't think short trips affect oil, but local journeys using lower gears more will cause more loads on bearing that does fail in Honda box. I have always put molyslip in my gearbox oil and my box went over 120K before I traded it in and gearbox still OK, my wifes Jazz got noisy at around 80K.