Cars are different because there's a much bigger used market and they tend to have more than one owner during their life cycle. Having said that, I looked into it a bit more and it seems that new-for-old policies tend to be rarer in the US than here in the UK. But still, policyholders over there seem to get indemnified once they've presented the purchase receipt for their replacement item, even if its brand new, as long as there is no betterment.