Members need to refresh their Actuarial Science Education [how insurance policies] are priced.
http://www.soa.org/
Warranties are just insurance policies either internally financed or created by a 3rd party.
The advantage the car manufacturer has is that they have a contractual labor discount with dealer. The dealer has agreed to fewer hours per repair than a paying customer would be charged based on a gigantic volume discount.
Third party service insurance policies try to get a discount from repair shop and require the use of used or non oem parts and many foolish shops go for it and many shops don't.
The technican gets stiffed paid for fewer hours! But some pay is better than no pay.
How the oem Nissan insurance can be priced lower yet deliver more to customer.
On a very big job like engine or transmission Nissan may drop ship new parts to dealer so dealer gets less parts profit than retail sales, again saving Nissan money.