Our insurance company depreciates seats as well. My seats had been made just over a year prior to the accident, but I had only bought them 6 months prior. So she used my receipt and have me full value rather than depreciating a year.
That being said, many other items are depreciated on a vehicle as well. For example struts and tires. Although they replaced with new parts in our vehicle, insurance takes off money for the wear and rear. So they measure tires and determine the wear and inspect struts for example. We paid the difference between the "worn value" and the new price on several parts. Many of the parts were unsafe to buy used and insurance will only replace with new parts. This is clear in our insurer's web site. Insurance costs would sky rocket if they didn't do this.
Long story for one example in our case. We had one damaged tire, with only 10% wear so they fully paid for ONE tire. Problem was, the manufacturer did not make our tires anymore and we could not buy just one. Any replacement tire was different tread, different rubber, etc. which would compromise the handling of our vehicle and also put uneven wear on the suspension. Both the tire manufacturer and vehicle manufacturer said it was unsafe to have mismatched tires on our vehicle and we had to pay for the other 3 new ones to have 4 matching tires. Insurance would not cover all 4 tires even though it was what was needed to have our vehicle safe on the road.
Do I think it's right? I'm not sure. I understand why insurance companies do it. I would have been paying higher rates all along otherwise. Maybe I evened out, maybe not.
ETA: it's typically insurance's job to put you back where you were before. Not worse and not better. This is why with parts that wear or have a lifespan, they depreciate them. Giving you something with more life than what you had would be putting you "better" than you were before at their expense.
And I grumbled more times than you can count when it happened to us as it cost us $1700 for upgrades to parts (darn fancy suspension system) and new tires. I'd have about flipped my lid if I'd have had my car seats depreciated too. Rubbing salt in the wound I tell ya!
