i've done 10,000 mile change intervals on a couple of cars... if the oil still looks and feels good, why drain it out and replace it?
i don't go by them, but if you have a newer vehicle with an oil life monitor, it will tell you to go about 10,000 miles if you do a lot of highway driving.. the one in my '01 GTP says that the oil life is at 65% after almost 5000 miles, and the 0W30 Mobil 1 still looks and feels almost as good as it did when i poured it in..