I Change my oil every 2500-3k miles. Yes, the oil is better, and could probably handle longer intervals... but only with the crud removed, stuff that the oil filter can't take out.
If I was running a bypass filter or centrifuge filter, I could see extending the drain interval, maby using synthetic as well. With a stock filter? Changing it on a regular basis is cheap insurance. It also keeps any leaked coolant from building up(note: you'll probably see it when removing the filter if any is leaking - makes interesting 'clean' spots on the metal 'grill' at the top of the filter).
I'M running Mobil Delvac 15w40 in my trucks; just watch for the mail-in rebates(currently at $35/5 gallons) and get it cheap!