Some things to be asked, Ford Man(thanks for sharing the experience by the way):
What is the shelf-life of motor oil anyway? 2, 3 years? How old is that Pennzoil stuff? Just a thought.
Have you always changed at 10k intervals? How do you drive your car MOST of the time, during any said interval?
Is it driven often? As in more than 2 or 3 times a week; not including short trips but actually getting up to operating tempt for a measurable amount of time/distance?
Did it ever have any major mechanic failures while in operation,(ever had overheating etc)? Did you stay on top of regular performance maintenance intervals as well? What is your climate conditions like year round? Have you towed much/ever with this vehicle?
All of these things are important to specify if another person chooses to start using conventional oil with any filter they can get and go 10k mile intervals. I wouldn't do that on that next generation V6 Stratus from the one I have(99 I-4) since it was prone to sludge and would suffer a pre-mature death.
Not that you are suggesting that, but some people could still run away with your experience, taking it out of prospective. I'm not familiar with your vehicle, but I wonder if they typically would last that long if cared for? Nice milestones.