26 psi is too low, in my opinion. I would go with about 32-35 psi. Reason? See Ford Explorer/Firestone fiasco. The main cause of those tire failures were most likely Ford's recommendation to run 26 psi in those tires (Ford changed the recommended pressure to 30 during the recall, still too low for such a heavy vehicle, in my opinion). They wanted to improve the ride, but failed to realize that that is too little tire pressure for a heavy SUV. Tires run at too low a pressure will overheat and at best wear out rapidly or at worst fail with catastrophic results.
Another possible cause for premature tire wear is being an overly enthusiastic driver. Rapid acceleration, hard braking, speeding, and fast cornering will greatly accelerate tire wear.
I like the seashell theory. It's completely ridiculous, but worth a chuckle. It's funny to me to hear the mechanical theories of a car-illiterate person. Don't feel bad if you bought it for a minute, the dealership should know their product. It doesn't mean they do, it just means that they should.