I think this says it best. It's from a random site I found
But as former service advisor David Langness put it, the 3,000-mile oil change is "a marketing tactic that dealers use to get you into the service bay on a regular basis. Unless you go to the drag strip on weekends, you don't need it."
Since Subaru has put the limit of oil changes at 7,500, and them probably knowing that people like to go over by some time because the service centres are full from everyone else rushing in for oil changes, it's probably safe to say that even at 7,500 there is still room left to play with. Manufactures will be on the safe side as they want to make sure they don't have to pay for a repair from their requirements.
If Audi is doing 10,000 and Porsche 911 turbo is at 15,000, these cars we have should be able to do 7,500 no problem.