The reason Ducati recommends the belts change every 12,000 mi/or 2 years, is because the tight radius of the cam pulleys tends to wear out the belts quicker than lets say a car timing belt. With the variability of tension settings and the normal reliability curve of any mechanical component, the recommended time/ mileage interval gives owner a good chance of not trashing the motor with a broken belt. The 2 year recommendation regardless of mileage is for the brittleness caused by the heat and the set the belt may take while not operating. I have seen belts with 18,000 miles look great, but have also heard of belts breaking with low mileage. It really comes down to how much you want to risk major engine work. I follow the factory recommendations and it gives me some piece of mind.