G-Man (do you have a name?):
You are probably right; I was referring to petroleum-based oils, not synthetics.
However, if you would just look at your oil (pull out the dipstick) at 3,000 miles, you will see that it is no longer clear, but now black. Not brown, not tan, but black. This does not mean that the oil has degraded, but rather that it is dirty. Why is it dirty? Because the combustion process creates particulant byproducts, and these are the things that can "ruin", or score, or affect, your engine.
There are reasons that detergent is used in all "oil" and gasoline products, and that is to keep injectors, valve, etc clean. But where do you think all this stuff that is being scrubbed off or from injectors are going? INTO YOUR OIL.
So, most of us who believe in the 3,000 oil change do so as VERY cheap insurance. In fact, if you do your own oil changes, it is only the cost of oil. And for 6 quarts at $1.50 per quart, how much insurance can you afford?
But I still don't understand why this is such an emotional subject!! It's as if so many people out there treat oil changes as a religion, and you all have read how religious wars can hurt innocent people. Let's just all of us get along, do our own thing about oil changes , and move on to really useful information about how to fix and maintain our wonderful Mercedeses.....Cheers, Andras