I too used to be paranoid about making sure my engine oil was changed. I still prefer an annual change, but there have been massive advances in the development of synthetic oils, which are also much much more expensive and completely different to mineral oils. I am no expert, but I do read, and these new oils can cover vast miles (200k in commercial situations) without a problem. There are other reasons vehicles need to be serviced , liability and health and safety are two, plus it is questionable whether the car buying public would believe it, which is probably the reason to stick with annual, or monitoring servicing.