When working as a performance engineer in the automotive industry, I have often did chemical analysis on motor oil of test vehicles every 5000 Km and even after 10000 Km of intensive testing (high engine load, high RPM...) the oil rarely got compromised.
Even the newest exotic vehicles now have service intervals up to 20000 Km.
My VW after 10k mi reccomends the oil change every 10k miles.