I also believe that new cars have longer oil change intervals to keep ownership costs "lower". When you see stuff like Consumers Reports statistics on ownership costs, some manufacture will do what it takes to get the costs down on paper. If car X's predicted yearly ownership costs are more than car Y's on paper then X will pinch some pennies to bring them down. If that means changing the oil every 15-20K than that's what they'll do. In the long run this is not an economical way to do things. But everything is disposable these days so it doesn't really matter. As long it's cheaper right here and now than that's good enough for most people. Sorry for being off topic.

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1967 200D FINTAIL (in service)- 86K
1983 VOLVO 244 DL (daily driver)- 300K
1988 VOLVO 244 DL (ice racer) - 345K