The thing is this isn't a defect. Say my brand new house came with a 40 gallon water tank and it failed (didn't flood, just stopped heating). The home warranty company provided a 45 gallon replacement. Nobody would expect that to be disclosed years down the line.
I think the difference is more in how you (or in this case the previous owner) sells it.
To stay with the water heater analogy - what if when the water heater needs to be replaced under warranty and the company says oh hey we have 40s in stock again so we're sending you what you should have had?
Whether or not they get the smaller units in stock, I don't have to let them into my house to install it, nor will a new owner of the home be expected to pay the difference between the 40 and 45. It's a permanent fixture. As is a battery in an electric car.
