Stated value is very different than agreed value, or as it is commonly referred to - True Agreed Value.
As plumcrazy said stated value still gives the insurance company wiggle room.
True agreed value means that there is no wiggle room. If you total the car they cut the check for the exact amount agreed on. You likely will not find this policy for most late model cars, because they are depreciating, and their value is bookable.
For rare classic cars, who's techinical book value is $500 but on the market is worth $100,000 and is likely appreciating rather than depreciating, True Agreed Value is the only way to go.
If anyone knows an insurer that would do a true agreed value policy on a late model Viper please post it here! Since what a great way for your car never to depreciate. Simply drive it for a few years and then go crash it, and you get all your money back.