Once a product leaves a distributor and is in the hands of a shipping company, it is completely out of the control of the distributor and in the care of the shipping company. This is the reason why the shipping company is legally responsible for shipping damage, not the distributor.
I can't even begin to count how many times I have read on woodworking forums people saying, "...don't ever buy an xxx-brand tool because mine got scratched or dented in transit." Instead of blaming the transit company that caused the problem and is liable for the problem, they blame the distributor. That is misplaced blame.
That's not something new. It is actually part of the legal system. Not knowing that is not an excuse in the legal sense.
Nevertheless, I bet if you check the paperwork that accompanied the shipment, you would actually find the wording that indicates the responsibility for inspecting shipping damage upon receipt. That wording doesn’t come from the distributor, it comes from the shipping company. When you accept a shipment without inspecting it for damage, you let the shipping company off the hook for their liability in making a claim. That's the reason why there is even a signature required in the first place.
When you sign, you are releasing them from claim. And if you look at the bottom of the form you signed upon receipt, you will probably see wording to that effect. (In other words, you signed a legal contract without reading it.)
When there is no visible exterior damage to the shipment, it can get a little dicey having the driver wait while you inspect. However, in your case, there was actual, visible exterior damage that should have prompted immediate inspection of the shipment upon arrival. The fact that your agent (wife or whomever) didn't do that is no one else's responsibility than your own.
By the way, the same conditions apply to the shipping company when they accept the shipment from the distributor in the first place. If they observe physical damage on a shipment before they take possession, they will either refuse to take the shipment, or document the damage as pre-existing. They do this because they know that they are on the hook for anything that happens while the shipment is in their possession.
You are attempting to blame someone else for your actions, or in this case, inactions. You need to take responsibility for your actions.