If you are claiming 6000 miles cause problems your claim is hogwash unless this is a Toyota dealership seeing a lot of those poorly designed Toyota v6's. For those, even a 3000 mile interval may not be often enough.
Jeff responds: If an engine is poorly designed, frequent oil changes won't prevent damage by the poor design. And poorly-designed engine will wear out just as quickly with 2000 mi oil change intervals as 6000 mi intervals. Actually, it will wear out faster. When oil filters are changed, the oil filter won't filter as effectively until some of the small holes in the filter media are closed off by dirt. So, until that happens, the oil will actually be dirtier than the oil going come out of an older filter.
The best thing to do for any engine is to change the oil when recommended, not after or before.
Jeff