I think telling people "if you cant afford that then you need to sell the truck to somebody that can properly take care of it. " is to extreme. It think it is up to the owner of the truck to decide what is 'proper' as they will have to pay for any damage that is caused. I think I should maintain my truck as well as I can, but if the engine blows because I don't change oil enough, I will have to pay for the rebuild or new engine. Just from the different opinions on this thread, I would say what is 'proper' is debatable.
The Freightliner truck I ran in 2002, 10K miles was less than a month. They changed oil every 15k, but they were newer engines, Detroit Series 60, 430hp.
Another thing that enters into it is the humidity of where you live. Here in the west, water in the oil is not as much of an issue. Dust and dirt are more of an issue. How hot your engine runs, and how hard your engine runs.
I do not think anyone wants to abuse their trucks, hence the original question.