Good points - like warminwisc posted the only real way to know how long of an interval is appropriate is to have the oil tested - a fairly easy procedure these days. Every car is gonna wear and degrade oil differently based on drivers habits, geo location, climate, and style of driving.

Also I have to say I am distrustful of the longer fluid change recommendations being put out there by the manufactures. There has been an ongoing competition between luxury brands for quite a few years to sell and market their cars as having very limited need for regular maintenance. As an example Lexus introduced "lifetime" AT fluid back in 04. They say you never have to change your AT fluid - only one problem they won't say exactly what they mean by "lifetime". My guess is that lifetime to any major corporation means something longer than normal warranty period and that's about it.

For my own financial good, and because I like to take really good care of my stuff, I learned long ago that inspecting and change all fluids regularly keeps the car like new and can save $ in the long run (and I mean all fluids - PS, AT, Brake, Coolant, Differential, Oil). JMHO and YMMV : )