Barry, I mean Luke, Should I be talking to the car or its owner. I am confused.
I am with KLC. My 2004 HCH owners manual calls for initial service/oil change at 10,000 miles, and every 10,000 thereafter. My dealer offered a free oil change/service at 5,000 (probably just to get me in the habit of letting them do it at 5,000 mile intervals). I took the free 5,000 mile change, and now I get it changed every 10,000 miles whether it needs it or not.
The dealer reminder sticker on the windshield tries to remind me to do it every 5,000, but I think that is just so they can double their share of my money.
If every 10,000 is what the factory says, then any less often would be ill advised. Any more often is, well, cautious. Nothing wrong with that, it is your money and your health, er, car.
I have never known a manufacturer to recommend maintenance less often than is advisable. Oh, maybe the less frequent maintenance schedule would be a selling point, but I don't know that anyone would buy a car for this reason unless it was every 100,000 miles or so. They may have an interest in your car dying early, but only if you are stupid enough to buy from the same manufacturer after the last car they sold you dies prematurely. On the other hand, they may want more frequent maintenance to put more money in the dealer's pockets, or to make their cars last longer and gain a good reputation for longevity and resale value, thus enhancing the brand image in the marketplace (but if every 10,000 miles is more frequent than necessary, I can live with that.)
It seems to me most likely, though, if the manufacturer suggests every 10,000 miles, then they probably know something about their design and the oil that will go into it.
Oil top up/change
