Going by my experience, Justin's probably right. I've owned (second hand ) two high-mileage cars : a 1990 Celica 1.8l with about 200k, and a 2002 protege with 160k. when choosing them, the one thing I looked for was regular oil changes, done according to schedule. Using the 2-cycle emissions test to guage wear, those engines had a projected life of about 30 years, even when the rest of the cars stopped working. The emissions were close to the minimums, and didn't really change.
My head says that as long as I stick to the manufacturers's grade, viscosity, and change interval specs, the nature of the oil does not matter.
Now, when it comes to my baby, the car that I plan to be in at my funeral, nothing says "I care" like full synthetic.