I feel as if 12.5 hrs a year of use is kind of low. I would think that I put at least 25 hours a year on my push mower when living in the city. But then again my lawn was fertilized, watered and cut every 3-4 days during the warm months. Either way, if what you state is correct, the engine might still outlast the transmission, wheels and deck on some of these machines. Many consumers just don't take care of their equipment.
Another thing that boggles my mind is that these engines would even consume oil at a rate fast enough to need topping off that frequently. I have never gone more than once season without changing the oil, but if from start to finish of each season I never consume any oil, I could theoretically go forever. . . . . . . . . . . . . . . without adding any.