I think it depends what type of oil you use. Synthetic can go longer between changes because it doesn't have viscosity modifiers that breakdown. For instance 5w-30 dyno oil is actually 5w oil with viscosity modifiers to make it act like 30 when hot. As the oil is churned about inside the engine, the modifiers break down until you're left with 5w oil that acts like 5w oil when hot (not good). Synthetic oil is different. The base stock of the oil is 5w-30 and doesn't break down to 5w with use, so you can go much longer between changes.
Synthetic oils are a whole different story. There is no VI improver added so there is nothing to wear out. The actual oil molecules never wear out. You could almost use the same oil forever. The problem is that there are other additives and they do get used up. I suppose if there was a good way to keep oil clean you could just add a can of additives every 6 months and just change the filter, never changing the oil.
I have seen several car owner manuals that are now stating that oils do not need to be changed but every 7,500 miles or more. The same manual also states OR every 12 months, whichever occurs first. My feeling is that you can probably go 5,000 miles on the average (in a sports car) but you must change your oil in the spring time at a minimum, particularly up north. Oils form waxes in icy cold weather. There is a permanent thickening of the oil.
Some automotive manufacturers are backing down on oil change intervals to 5,000 miles or less and some advocate changing the oil at least every 6 months as well. I think this is because of the tendency for oils to thicken in very hot engines (not ambient conditions, just hot engines). Also because of thickening from the cold of winter and from sludge build up that cannot be filtered out.