Highway miles are easier on oil, as others have said. Short trips (particularly in cold weather) are the hardest on oil. I wouldn't change your oil until the normal interval.
As far as idling before driving off and after stopping, 10-20 seconds is really not "idling". Idling before shutdown is solely to cool turbo, idling for warm-up is generally considered a waste of fuel, and prolonging the engine from getting up to temp. That said, I personally ensure my vehicles are somewhat warmed up prior to being placed under heavy load (towing, plowing, interstate, etc).
