I would guess that for the Mercedes engine they do recommend synthetic oil, which is why they also recommend 10,000 oil changes. Oil change intervals in Europe typically run double what we do on this side of the pond. As an experiment, I changed the oil on my new 2001 Silverado with a 5.3 engine at 2,500 miles with Mobil 1 and a Mobil 1 oil filter, and at every 10,000 mile interval after that. I am now ready to break the 170,000 miles mark, and the engine is still going strong. It uses about a quart of oil every 10,000 miles, which it did from when it was new. I agree that changing it every 5,000 is cheap insurance - I just wanted to see what would happen if I went 10,000 between changes.